NXTM Nxstage Medical, Inc.

PROPOSAL 5 — APPROVAL OF AMENDMENT TO OUR BY-LAWS TO ADOPT MAJORITY

VOTING STANDARD IN UNCONTESTED DIRECTOR ELECTIONS

Under our Amended and Restated By-laws (By-laws), directors are currently elected by a plurality vote. Under this standard, director nominees with the most votes cast in their favor are elected, up to the number of directors to be elected at a meeting, notwithstanding any withheld votes.

Our Board recommends that our By-laws be amended to change the voting standard for the election of directors in uncontested elections from a plurality standard to a majority standard. Under the proposed majority voting standard, a nominee for director in an uncontested election will be elected to our Board if the votes cast for such nominee’s election exceed the votes cast against such nominee’s election. Under Delaware law, an incumbent director who fails to receive the vote required for reelection “holds over,” or continues to serve as a director until his or her successor is elected and qualified, or until his or her earlier resignation or removal. To address the “hold over” issue, the proposed By-law amendment provides that an incumbent director who does not receive the number of votes required for reelection must promptly tender his or her resignation. Our Board would then need to determine whether to accept or reject the resignation within 90 days after certification of the election results and publicly disclose its decision in a filing with the SEC. In contested elections, where the number of nominees exceeds the number of directors to be elected, the plurality standard would continue to apply and the nominees receiving the most votes would be elected.

If the proposed By-law amendment is not approved, the existing plurality voting standard in our By-laws will remain in effect.

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In furtherance of our commitment to strong corporate governance and to ensuring that stockholders are afforded a meaningful role in the election of directors, our Board has approved and recommends that our stockholders vote in favor of the proposed By-law amendment. Our Board also recognizes that a majority voting standard will preclude the election of directors who do not have broad acceptance among our stockholders and may enhance each director’s accountability to our stockholders. As a result, our Board has determined that a majority voting standard for uncontested elections for directors would be in the best interests of NxStage and our stockholders. At our 2014 annual meeting of stockholders, we similarly proposed a By-law amendment to adopt a majority voting standard in uncontested director elections, and while holders of 72% of our then-outstanding shares voted for that proposal, those votes did not meet the approval threshold (75% of our outstanding shares) required by our Restated Certificate of Incorporation.

If approved, the By-law amendment would be effective immediately. The new majority voting standard would be applicable to the election of our directors at the 2018 annual meeting of stockholders (if uncontested) and to any earlier uncontested election of directors occurring after the amendment becomes effective.

The proposed By-law amendment is set forth in Appendix A to this proxy statement. Stockholders should refer to Appendix A for the full text of the proposed By-law amendment.

Our Board recommends a vote FOR the amendment to our Amended and Restated By-laws to adopt a majority voting standard for uncontested director elections.

PROPOSAL 6 — APPROVAL OF OUR AMENDED AND RESTATED 2014 OMNIBUS INCENTIVE

PLAN AND §162(m) MATERIAL TERMS

We are asking our stockholders to consider and to approve the NxStage Medical, Inc. Amended and Restated 2014 Omnibus Incentive Plan (2014 Plan or Amended and Restated 2014 Plan) set forth in Appendix B to this proxy statement. Upon recommendation of our Compensation Committee, our Board adopted the 2014 Plan on April 14, 2017, to be effective upon approval by our stockholders at the Annual Meeting.

Our Board has proposed approval of the 2014 Plan by our stockholders, among other things, to:

Our Board believes that the 2014 Plan promotes the interests of our stockholders and is consistent with principles of good corporate governance, including the following:

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We are asking our stockholders to approve the 2014 Plan in order to comply with applicable NASDAQ rules and to allow our Compensation Committee to grant, if desired, performance-based compensation that is exempt from the deduction limitations under §162(m) of the Code. Section 162(m) generally provides that compensation paid by a publicly-held corporation to its “covered employees” (the corporation’s chief executive officer together with its three most highly-paid named executive officers other than its chief financial officer) is not deductible by the corporation for U.S. federal income tax purposes for any taxable year to the extent it exceeds $1 million. This limitation does not apply to compensation that qualifies as exempt performance-based compensation by meeting certain requirements under §162(m), including the requirement that the material terms of the related performance goals be disclosed to and approved by the corporation’s stockholders not less frequently than every five years. Under §162(m), the material terms include the class of eligible employees, a description of the business criteria on which the performance goals may be based and the maximum amount that can be paid to any participant for a specified period. For the 2014 Plan, these terms are described below under “Eligibility,” “Performance Measures” and “Maximum Payment to Eligible Persons,” respectively. Although stockholder approval is one of the requirements for exemption under §162(m), even with stockholder approval, there can be no guarantee that compensation will be treated as exempt performance-based compensation. Furthermore, our Compensation Committee will continue to have the authority under the 2014 Plan to provide compensation that is not exempt from the limits on deductibility under §162(m).

The Amended and Restated 2014 Plan will become effective on the date it is approved by our stockholders, if it is approved by our stockholders. If our stockholders do not approve the Amended and Restated 2014 Plan, compensatory equity-based grants to our key personnel will continue to be made under the present version of the NxStage Medical, Inc. 2014 Omnibus Incentive Plan to the extent of the shares of common stock that remain available for issuance and we will have a limited time available to grant awards, if desired, that constitute performance-based compensations exempt from the deduction limitations under §162(m) of the Code.

Our Board believes that approval of the 2014 Plan is in the best interests of NxStage and our stockholders by allowing us to continue to grant equity-based compensation to our key personnel. Our Board believes that the achievement of long-term objectives and employee retention are fostered through equity awards that vest over time. By approving the 2014 Plan, our stockholders will enable us to continue offering a competitive compensation package that is linked to our common stock performance and to continue recruiting and retaining highly-qualified officers, employees, non-employee directors and key advisers. Our Board believes that if this proposal is not approved, our ability to align the interests of key personnel with stockholders through equity-based compensation would be compromised, which would disrupt our compensation program and impair our ability to recruit and retain key personnel. In addition, if we could not offer equity compensation, we would have to increase our use of cash compensation which could have an adverse impact on our business plans and operations.

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Equity Utilization

If approved by stockholders, the 2014 Plan would make an additional 6,300,000 shares of our common stock available for future grants. We believe that this represents an appropriate share increase at this time. In determining the number of shares to make available under the 2014 Plan, our Board and Compensation Committee considered a number of factors, including:

In addition, Radford, our Compensation Committee’s independent compensation consultant, reviewed the share request in the context of NxStage’s business needs and advised our Compensation Committee that such request should be considered reasonable when compared to peer group practices, broader industry practices and proxy advisory firm guidelines. Based on their assessment of the foregoing factors, our Compensation Committee recommended and our Board approved the proposed increase to the share pool under the 2014 Plan to ensure that we continue to have the ability to provide industry competitive long-term incentive compensation.

Based on these same factors, we estimate that the availability of 6,300,000 shares, plus up to 1,510,752 shares available for grant under the 2014 Plan as of March 20, 2017 (Measurement Date), will provide a sufficient additional number of shares to enable us to continue to make equity awards at our historical average annual rates for the next three to four years. As of the Measurement Date, we had the following outstanding grants under the 2014 Plan:

As of the Measurement Date:

We also maintain a tax-qualified employee stock purchase plan, pursuant to which 207,911 shares remain available for issuance as of the Measurement Date.

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Our rates of equity grants and forfeitures during the past three years are summarized in the following table:

Awards under the 2014 Plan would continue to be granted at the discretion of our Compensation Committee. As of the date of this proxy statement, future awards under the 2014 Plan have not been determined. We use equity as part of our compensation program to achieve a number of important goals, including aligning the interests of our key personnel with appropriate business risk and the long-term interests of our stockholders, conserving cash and providing true “pay for performance” by putting a significant portion of our key personnel’s pay at risk and directly linking the realized value of awards to our stock price. The size of equity awards is based on a number of factors, including the individual’s performance, the amount of equity previously awarded to the individual, retention considerations, the vesting of such awards, management recommendations and peer group data. Our Compensation Committee delivers long-term performance-based compensation to our named executive officers through annual grants of performance shares and stock options. The total value for such performance-based compensation is split equally between grants of stock options and performance shares to align our equity compensation program with peer group and broader industry practices and to promote both near- and long-term value creation for our stockholders. Because performance shares are so-called “full value” awards (delivering a share without payment of an exercise price), we generally grant significantly fewer performance shares than the number of stock options we would grant for a similar purpose. For additional information about how we use equity instruments to achieve the objectives of our executive compensation program, please read the  Compensation Discussion and Analysis  section of this proxy statement.

Principles of the 2014 Plan

The 2014 Plan is intended to (1) provide eligible persons with an incentive to contribute to the success of NxStage and to operate and manage our business in a manner that will provide for our long-term growth and profitability to benefit our stockholders and other important stakeholders, including our employees and customers, and (2) provide a means of recruiting, rewarding and retaining key personnel. To this end, the 2014 Plan provides for the grant of stock options, stock appreciation rights, restricted stock, restricted stock units, unrestricted stock, dividend equivalent rights, performance shares and other performance-based awards, other equity-based awards, and cash awards. Any of these awards may, but need not, be made as performance incentives to reward attainment of annual or long-term performance goals in accordance with the terms of the 2014 Plan. Stock options granted under the 2014 Plan may be non-qualified stock options or incentive stock options, except that incentive stock options are only available to our employees.

Description of the 2014 Plan

A summary of the material terms of the 2014 Plan is set forth below. This summary, however, does not purport to be a complete description of all of the provisions of the 2014 Plan and is qualified in its entirety by reference to the full text of the 2014 Plan, a copy of which is attached as Appendix B to this proxy statement and which is incorporated by reference into this proposal. Stockholders should refer to Appendix B for a more complete description of the 2014 Plan.

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Effective Date and Term.     The present version of the NxStage Medical, Inc. 2014 Omnibus Incentive Plan became effective on May 22, 2014 and will expire on May 21, 2024, with the changes reflected by the amendment and restated of the plan being subject to and effective as of stockholder approval at the Annual Meeting.

Administration of the 2014 Plan.     The 2014 Plan is administered by our Compensation Committee, and our Compensation Committee determines all terms of awards under the 2014 Plan. During any period of time in which we do not have a compensation committee, the 2014 Plan will be administered by our Board or another committee appointed by our Board. In addition, subject to the 2014 Plan and applicable law, (1) our Board retains the authority under the 2014 Plan to exercise any or all of the powers and authorities related to the administration and implementation of the 2014 Plan and (2) our Compensation Committee may delegate to a designated officer the power and authority to grant awards to non-executive employees. References below to our “Compensation Committee” include a reference to our Board, another committee appointed by our Board, or the designated officer for those periods in which our Board, such other committee appointed by our Board, or such designated officer is acting.

Except where the authority to act on such matters is specifically reserved to our Board under the 2014 Plan or applicable law, our Compensation Committee has full power and authority to interpret and construe all terms of the 2014 Plan, any award, or any award agreement, and to make all related determinations, including the power and authority to:

Awards.     The following types of awards may be made under the 2014 Plan, subject to the limitations set forth in the 2014 Plan:

The 2014 Plan provides that each award will be evidenced by an award agreement, which may specify terms and conditions of the award that differ from the default terms and conditions under the 2014 Plan. Awards under the 2014 Plan may be granted alone or in addition to, in tandem with, or in substitution or exchange for any other award under the 2014 Plan, other awards under another compensatory plan of NxStage or any of its affiliates (or any business entity that has been a party to a transaction with NxStage or any of its affiliates), or other rights to payment from NxStage or any of its affiliates. Awards granted in addition to or in tandem with other awards may be granted either at the same time or at different times. Our Compensation Committee may permit or require the

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deferral of any payment pursuant to any award into a deferred compensation arrangement, which may include provisions for the payment or crediting of interest or dividend equivalent rights, in accordance with rules and procedures established by our Compensation Committee. Awards under the 2014 Plan generally are granted for no consideration other than services provided by the recipient.

Eligibility.     Employees and non-employee directors of NxStage and its affiliates are eligible to receive awards under the 2014 Plan. As of the date of this proxy statement, approximately 510 individuals hold awards under the present version of the NxStage Medical, Inc. 2014 Omnibus Incentive Plan and our compensation programs contemplate that approximately 450 individuals may become eligible to receive future awards under the 2014 Plan, in each instance including our five executive officers and eight non-employee directors. In addition, key consultants and advisors who perform services for NxStage or its affiliates may receive awards under the 2014 Plan.

Non-Employee Director Limits .    The aggregate value of all compensation granted or paid to any non-employee director with respect to any calendar year, including awards granted under the 2014 Plan and cash fees or other compensation paid by NxStage to such non-employee director outside of the 2014 Plan, in each case for his or her services as a non-employee director during such calendar year, may not exceed $600,000 in the aggregate.

Share Authorization and Usage.     As of the date of this proxy statement, the maximum number of shares of common stock that may be issued in the future under the present version of the NxStage Medical, Inc. 2014 Omnibus Incentive Plan, consisting of authorized but unissued shares, is 1,523,005 shares of common stock. An additional 6,300,000 shares of common stock may be issued in the future under the 2014 Plan if it is approved by our stockholders. The maximum number of shares of common stock available for issuance pursuant to incentive stock options granted under the 2014 Plan will be the same as the number of shares of common stock available for issuance under the 2014 Plan.

Shares of common stock that are subject to awards other than stock options or stock appreciation rights are presently counted against the NxStage Medical, Inc. 2014 Omnibus Incentive Plan share limit as 1.62 shares for every one share subject to the award. If approved by our stockholders, the additional 6,300,000 shares of common stock under the Amended and Restated 2014 Plan would be subject to a utilization rate of 1.96 shares for similar awards. Shares of common stock that are subject to awards of stock options or stock appreciation rights are counted against the 2014 Plan share limit as one share for every one share subject to the award. The number of shares subject to any stock appreciation rights awarded under the 2014 Plan are counted against the aggregate number of shares available for issuance under the 2014 Plan regardless of the number of shares actually issued to settle the stock appreciation right upon exercise.

If any awards under the 2014 Plan terminate, expire, or are canceled, forfeited, exchanged, or surrendered without having been exercised or paid or if any awards under the 2014 Plan are forfeited or expire or otherwise terminate without the delivery of any shares of common stock, the shares subject to such awards will again be available for purposes of the 2014 Plan in the same amount as such shares were counted against the share limit. However, the number of shares of common stock available for issuance under the 2014 Plan will not be increased by the number of shares of common stock (1) tendered or withheld in connection with the purchase of shares of common stock upon, or our tax withholding obligations arising from, exercise of a stock option or stock appreciation right or (2) purchased by us with the proceeds from stock option exercises.

The number and kinds of shares of common stock for which awards may be made under the 2014 Plan, including the limit described above and the performance-based limits described below, will be adjusted proportionately and accordingly by our Compensation Committee if the number of outstanding shares of common stock is increased or decreased or the shares of common stock are changed into or exchanged for a different number of shares or kind of capital stock or other securities of NxStage on account of any recapitalization, reclassification, stock split, reverse stock split, spin-off, combination of stock, exchange of stock, stock dividend, or other distribution payable in capital stock, or other increase or decrease in shares of common stock effected without receipt of consideration by NxStage.

Fair Market Value Determination.     For so long as our common stock remains listed on the NASDAQ Stock Market (or listed on another established national or regional stock exchange or traded on another established securities market), the fair market value of a share of common stock will be the closing price for a

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share as quoted on such exchange or market for such date. If there is no reported closing price on such date, the fair market value of a share of common stock will be the closing price of the common stock on the next preceding date for which such quotation exists. On April 19, 2017, the closing price of our common stock as reported on the NASDAQ Stock Market was $27.38 per share.

If our common stock is not listed on an established national or regional stock exchange or traded on another established securities market, our Compensation Committee will determine the fair market value by the reasonable application of a reasonable valuation method, in a manner consistent with §409A of the Code.

No Repricing .    Except in connection with a corporate transaction involving NxStage (including any stock dividend, distribution of cash, common stock, other securities, or other property, stock split, extraordinary cash dividend, recapitalization, change in control, reorganization, merger, consolidation, split-up, spin-off, combination, repurchase or exchange of common stock or other securities, or similar transaction), we may not, without obtaining stockholder approval, (1) amend the terms of outstanding stock options or stock appreciation rights to reduce the exercise price of such outstanding stock options or stock appreciation rights, (2) cancel outstanding stock options or stock appreciation rights in exchange for stock options or stock appreciation rights with an exercise price that is less than the exercise price of the original stock options or stock appreciation rights or (3) cancel outstanding stock options or stock appreciation rights with an exercise price above the current fair market value of a share of common stock in exchange for cash or other securities.

Stock Options .    The 2014 Plan permits our Compensation Committee to grant incentive stock options (under §422 of the Code) and stock options that do not qualify as incentive stock options. The exercise price of each stock option will be determined by our Compensation Committee; provided, that the exercise price cannot be less than 100% of the fair market value of a share of our common stock on the date on which the stock option is granted.

The term of a stock option cannot exceed ten years from the date of grant. Our Compensation Committee determines at what time or times each stock option may be exercised and the period of time, if any, after retirement, death, disability, or termination of employment during which stock options may be exercised. Stock options may be made exercisable in installments.

To the extent that the aggregate fair market value of shares of common stock determined on the date of grant with respect to which incentive stock options are exercisable for the first time during any calendar year exceeds $100,000, the stock option will be treated as a non-qualified stock option.

Awards of stock options are nontransferable, except (1) for transfers by will or the laws of descent and distribution or (2) if authorized in the applicable award agreement, for transfers of non-qualified stock options, not for value, to family members and related trusts pursuant to the terms and conditions of the 2014 Plan.

Stock Appreciation Rights .    The 2014 Plan permits our Compensation Committee to grant stock appreciation rights, which are a right to receive a number of shares or, in the discretion of our Compensation Committee, an amount in cash or a combination of shares and cash, based on the increase in the fair market value of the shares of our common stock underlying the right during a stated period specified by our Compensation Committee. Stock appreciation rights may be granted in conjunction with all or a part of any stock option or other award granted under the 2014 Plan, or without regard to any stock option or other award. Our Compensation Committee will determine at the stock appreciation right grant date or thereafter the time or times at which and the circumstances under which a stock appreciation right may be exercised in whole or in part, the time or times at which and the circumstances under which a stock appreciation right will cease to be exercisable, the method of exercise, the method of settlement, the form of consideration payable in settlement, the method by which shares of our common stock will be delivered or deemed delivered to recipients, and any other terms or conditions of any stock appreciation right. Exercisability of stock appreciation rights may be subject to future service requirements, to the achievement of one or more of the performance measures described below, or to such other terms and conditions as our Compensation Committee may impose.

Upon exercise of a stock appreciation right, the holder will be entitled to receive, in the specified form of consideration, the excess of the fair market value of one share of our common stock on the exercise date over the exercise price of the stock appreciation right, as determined by our Compensation Committee. The exercise price of the stock appreciation right may not be less than the fair market value of a share of our common stock on the grant date.

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Awards of stock appreciation rights are nontransferable, except (1) for transfers by will or the laws of descent and distribution, or (2) if authorized in the applicable award agreement, not for value, to family members and related trusts pursuant to the terms and conditions of the 2014 Plan.

Restricted Stock and Restricted Stock Units .    The 2014 Plan permits our Compensation Committee to grant restricted stock and restricted stock units. Subject to the provisions of the 2014 Plan, our Compensation Committee determines the terms and conditions of each award of restricted stock and restricted stock units, including the restricted period for all or a portion of the award, the restrictions applicable to the award, and the purchase price (if any) for the shares of common stock subject to the award. Restricted stock and restricted stock units may vest solely by the passage of time or pursuant to achievement of performance goals, and the restrictions and the restricted period may differ with respect to each award of restricted stock and restricted stock units. An award will be subject to forfeiture if events specified by our Compensation Committee occur before the lapse of the restrictions. A recipient of restricted stock will have all the rights of a stockholder, including the right to vote the shares, except to the extent limited by our Compensation Committee. Recipients of restricted stock units will have no voting rights or other rights associated with share ownership and no dividends will be payable with respect to any unvested awards.

During the period, if any, when stock awards are non-transferable or forfeitable or prior to the satisfaction of any other restrictions prescribed by our Compensation Committee, a participant is prohibited from selling, transferring, assigning, pledging, or otherwise encumbering or disposing of his or her shares of restricted stock or restricted stock units.

Forms of Payment .    The exercise price for any stock option or the purchase price (if any) for restricted stock is generally payable (1) in cash or cash equivalents, (2) to the extent the award agreement provides, by the surrender of shares of common stock with an aggregate fair market value, on the date on which the stock option is exercised, equal to the exercise price, (3) to the extent permissible by applicable law and to the extent the award agreement provides, by payment through a broker in accordance with procedures set forth by us, or (4) to the extent the award agreement provides, any other form permissible by applicable laws, including net exercise.

Dividend Equivalent Rights.     The 2014 Plan permits our Compensation Committee to grant dividend equivalent rights, which are rights entitling the recipient to receive credits for cash distributions that would be paid if the recipient had held a specified number of shares of common stock underlying the right. Our Compensation Committee may grant rights to dividend equivalents to a recipient in connection with an award under the 2014 Plan, or without regard to any other award, except that no dividend equivalent right may be granted in connection with, or related to, a stock option or stock appreciation right. The terms and conditions of awards of dividend equivalent rights will be specified in the applicable award agreement.

Dividend equivalents credited to the holder of a dividend equivalent right may be paid currently (with or without being subject to forfeiture or a repayment obligation) or may be deemed to be reinvested in additional shares of common stock, which may thereafter accrue additional dividend equivalent rights (with or without being subject to forfeiture or a repayment obligation). Any such reinvestment will be at the fair market value of our common stock on the reinvestment date. Dividend equivalent rights may be settled in cash, shares of our common stock, or a combination thereof, in a single installment or in multiple installments, as determined by our Compensation Committee.

A dividend equivalent right granted as a component of another award may provide that the dividend equivalent right will be settled upon exercise, settlement, or payment of, or lapse of restrictions on, the other award, and that the dividend equivalent right will expire or be forfeited under the same conditions as the other award. A dividend equivalent right granted as a component of another award also may contain terms and conditions that are different from the terms and conditions of the other award.

Performance-Based Awards .    The 2014 Plan permits our Compensation Committee to grant performance-based awards, ultimately payable in shares of our common stock or cash, in such amounts and upon such terms as determined by our Compensation Committee. Each grant of a performance-based award will have an initial cash value or an actual or target number of shares of common stock that is established by our Compensation Committee at the time of grant. Our Compensation Committee may set performance goals in its discretion that, depending on the extent to which they are met, will determine the value or number of performance-based awards

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that will be paid out to a recipient. The performance goals generally will be based on one or more of the performance measures described below. Our Compensation Committee will establish the performance periods for these performance-based awards. As described below, the 2014 Plan is designed to permit our Compensation Committee to grant awards that qualify as performance-based for purposes of satisfying the conditions of §162(m) of the Code.

Unrestricted Stock .    The 2014 Plan permits our Compensation Committee to grant (or sell at the par value of a share of our common stock or such other higher purchase price determined by our Compensation Committee) an award to any recipient pursuant to which such recipient may receive shares of our common stock free of any restrictions under the 2014 Plan.

Other Equity-Based Awards.     The 2014 Plan permits our Compensation Committee to grant other types of stock-based awards under the 2014 Plan. The terms and conditions that apply to other equity-based awards are determined by our Compensation Committee and may be granted with vesting, value, and payment contingent upon the achievement of one or more performance goals.

Recoupment.     Any award granted pursuant to the 2014 Plan, together with the proceeds from the exercise or disposition of such award, is subject to mandatory repayment by the recipient to us to the extent required by any law, rule, or regulation which imposes mandatory recoupment, under circumstances set forth in such law, rule, or regulation.

Change in Control .    If NxStage experiences a change in control, as defined below, the following provisions will apply unless otherwise provided in an award agreement:

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A change in control occurs under the 2014 Plan if:

Amendment and Termination .    Our Board may amend, suspend, or terminate the 2014 Plan at any time; provided, that with respect to awards already granted under the 2014 Plan, no amendment, suspension, or termination of the 2014 Plan will, without the consent of the recipient, materially impair the rights under any such award. Our stockholders must approve any amendment if such approval is required under applicable law or stock exchange requirements and must approve any amendment that changes the no-repricing provisions of the 2014 Plan.

Section 162(m) Performance-Based Compensation Terms

Stockholder approval of this proposal is also intended to allow us to grant stock-based awards and cash incentive compensation paid to our covered executive officers under the 2014 Plan that is intended to constitute qualified performance-based compensation for purposes of §162(m) of the Code, if desired. Stockholder approval of this proposal will constitute approval of the §162(m) performance-based compensation terms described below, which consist of provisions relating to (1) the persons eligible to receive performance-based compensation under the 2014 Plan, (2) the maximum amount of performance-based compensation that may be paid under the 2014 Plan during a specified period to any eligible person, and (3) the performance criteria that may be used under the 2014 Plan to establish performance goals as a condition to the payment of the performance-based awards. However, even if this proposal is approved, our Compensation Committee may exercise its discretion to award compensation under the 2014 Plan that would not qualify as qualified performance-based compensation under §162(m) of the Code, and in doing so may in its discretion choose not to attach any performance-based criteria to an award or choose to employ performance criteria that are not among the list of performance goals set forth below.

Maximum Payment to Eligible Persons.     The 2014 Plan contains limitations on the number of shares of common stock available for issuance with respect to specified types of awards. The maximum number of shares of common stock subject to stock options or stock appreciation rights that may be issued under the 2014 Plan to any person is 1,000,000 shares in any single calendar year. The maximum number of shares of common stock that may be issued under the 2014 Plan to any person pursuant to an award other than a stock option or stock appreciation right is 1,000,000 shares in any single calendar year. The maximum amount that may be paid as a

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cash-denominated performance-based award (whether or not cash-settled) for a performance period of 12 months or less to any person eligible for an award is $3,000,000, and the maximum amount that may be paid as a cash-denominated performance-based award (whether or not cash-settled) for a performance period of greater than 12 months to any person eligible for an award is $5,000,000.

Performance Measures.     The 2014 Plan authorizes the establishment of performance goals based on any one or more of the following performance measures:

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The 2014 Plan identifies some conditions that may warrant revision or alteration of performance goals after they are established by our Compensation Committee. Such conditions may include the following:

Performance under any of the foregoing performance measures may be used to measure the performance of (1) NxStage and its subsidiaries and other affiliates as a whole; (2) NxStage, any subsidiary, or any other affiliate or any combination thereof; or (3) any one or more business units, operating segments or geographic areas of NxStage, any subsidiary, or any other affiliate, as our Compensation Committee deems appropriate. In addition, performance under any of the performance measures may be compared to the performance of one or more other companies or one or more published or special indices designated by our Compensation Committee and may be

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measured based on absolute numbers or rates of growth or reduction in the applicable measure. Our Compensation Committee has the authority to provide for accelerated vesting of any performance-based award based on the achievement of performance goals pursuant to the performance measures. Our Compensation Committee has the discretion to adjust awards that are intended to qualify as performance-based compensation, either on a formula or discretionary basis, or on any combination thereof, as our Compensation Committee determines appropriate.

Federal Income Tax Consequences

The federal income tax consequences of awards under the 2014 Plan for participants and NxStage will depend on the type of award granted. The following description of tax consequences is intended only for the general information of stockholders. A participant in the 2014 Plan should not rely on this description and instead should consult his or her own tax advisor.

Incentive Stock Options .    The grant of an incentive stock option will not be a taxable event for the recipient or for NxStage. A recipient generally will not recognize taxable income upon exercise of an incentive stock option (except that the alternative minimum tax may apply), and any gain realized upon a disposition of the shares of common stock received pursuant to the exercise of an incentive stock option will be taxed as long-term capital gain if the recipient holds the shares of common stock for at least two years after the date of grant and for one year after the date of exercise (holding period requirement). NxStage will not be entitled to any business expense deduction with respect to the exercise of an incentive stock option, except as discussed below.

For the exercise of an incentive stock option to qualify for the foregoing tax treatment, except in the case of the recipient’s death or disability, the recipient generally must be an employee of NxStage or our subsidiaries from the date the option is granted through a date within three months before the date of exercise of the option.

If all of the foregoing requirements are met except the holding period requirement mentioned above, the recipient will recognize ordinary income upon the disposition of the shares of our common stock in an amount generally equal to the excess of the fair market value of the shares of our common stock at the time the option was exercised over the exercise price (but not in excess of the gain realized on the sale). The balance of the realized gain, if any, will be capital gain. NxStage will generally be allowed a business expense deduction to the extent the recipient recognizes ordinary income.

Non-Qualified Stock Options.     The grant of a non-qualified stock option will not be a taxable event for the recipient or NxStage. Upon exercising a non-qualified stock option, a recipient will recognize ordinary income in an amount equal to the difference between the exercise price and the fair market value of the shares of our common stock acquired on the date of exercise. A corresponding deduction is generally available to NxStage. Upon a subsequent sale or exchange of the shares of our common stock acquired pursuant to the exercise of a non-qualified stock option, any recognized gain or loss to the recipient is treated as a capital gain or loss for which NxStage is not entitled to a deduction.

Stock Appreciation Rights.     There are no immediate tax consequences of receiving an award of stock appreciation rights under the 2014 Plan. Upon exercising a stock appreciation right, a recipient will recognize ordinary income in an amount equal to the cash or the fair market value of the common stock received by the recipient. NxStage will be entitled to a deduction equal to the amount of any compensation income taxable to the recipient.

Restricted Stock .    A recipient of restricted stock will not recognize any taxable income for federal income tax purposes in the year of the award, provided that the shares of our common stock are subject to restrictions (that is, the restricted stock is nontransferable and subject to a substantial risk of forfeiture). The recipient, however, may elect under §83(b) of the Code to recognize compensation income in the year of the award in an amount equal to the fair market value of the shares of our common stock on the date of the award (less the purchase price, if any), determined without regard to the restrictions. If the recipient does not make such a §83(b) election, the fair market value of the shares of common stock on the date the restrictions lapse (less the purchase price, if any) will be treated as compensation income to the recipient and will be taxable in the year the restrictions lapse. NxStage will generally be entitled to a business expense deduction in the same amount and

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generally at the same time as the recipient recognizes ordinary income. If a participant makes an effective §83(b) election, no additional income results by reason of the lapsing of the restrictions.

For purposes of determining capital gain or loss on a sale of shares awarded under the 2014 Plan, the holding period in the shares begins when the recipient recognizes taxable income with respect to the transfer. The recipient’s tax basis in the shares equals the amount paid for the shares plus any income realized with respect to the transfer. However, if a recipient makes an effective §83(b) election and later forfeits the shares, the tax loss realized as a result of the forfeiture is limited to the excess of what the recipient paid for the shares (if anything) over the amount (if any) realized in connection with the forfeiture.

Restricted Stock Units.     There are no immediate tax consequences of receiving an award of restricted stock units under the 2014 Plan. A distribution of shares of our common stock or a payment of cash in satisfaction of restricted stock units will be taxable as ordinary income when the distribution or payment is actually or constructively received by the recipient. The amount taxable as ordinary income is the aggregate fair market value of the shares of our common stock determined as of the date they are received or, in the case of a cash award, the amount of the cash payment. NxStage will generally be entitled to a business expense deduction in the same amount and generally at the same time as the recipient recognizes ordinary income.

Dividend Equivalent Rights .    A recipient of dividend equivalent rights will be required to recognize ordinary income in an amount distributed to the recipient pursuant to the award. NxStage will generally be entitled to a business expense deduction in the same amount and generally at the same time as the recipient recognizes ordinary income.

Performance-Based Awards .    The award of a performance or annual incentive award will have no federal income tax consequences for us or for the recipient. The payment of the award is taxable to a recipient as ordinary income. NxStage will generally be entitled to a business expense deduction in the same amount and generally at the same time as the recipient recognizes ordinary income.

Unrestricted Stock .    A recipient of unrestricted stock will be required to recognize ordinary income in an amount equal to the fair market value of the shares of our common stock on the date of the award, reduced by the amount, if any, paid for such shares. NxStage will generally be entitled to deduct the amount of any compensation income taxable to the recipient.

Upon the recipient’s disposition of unrestricted stock, any gain realized in excess of the amount reported as ordinary income will be reportable by the recipient as a capital gain, and any loss will be reportable as a capital loss. Capital gain or loss will be long-term if the recipient has held the shares for more than one year. Otherwise, the capital gain or loss will be short-term.

New Plan Benefits

Our Compensation Committee has not granted any awards under the Amended and Restated 2014 Plan which is the subject of stockholder approval under this Proposal 6. For a description of awards granted to our named executive officers during 2016, please see the 2016 Grants of Plan-Based Awards table below.

Registration with the SEC

If the 2014 Plan is approved by our stockholders, we intend to file a Registration Statement on Form S-8 relating to the additional shares authorized under the 2014 Plan with the SEC pursuant to the Securities Act.

Our Board recommends a vote FOR approval of the NxStage Medical, Inc. Amended and Restated 2014 Omnibus Incentive Plan and the material terms of this plan for purposes of §162(m) of the Code.

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STOCK OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

The following table and accompanying notes provide information about the beneficial ownership of our common stock by:

Beneficial ownership is determined in accordance with the rules of the SEC, and the information is not necessarily indicative of beneficial ownership for any other purpose. Under these rules, beneficial ownership includes any shares as to which the person has sole or shared voting and investment power and also includes any shares that the person has the right to acquire within 60 days after April 18, 2017 (Ownership Date) through the exercise of any stock option, warrant or right, through conversion of any security, or pursuant to the automatic termination of power of attorney or revocation of trust, discretionary account or similar arrangement. Unless otherwise indicated, the persons identified have sole voting and investment power with respect to the shares of our common stock set forth below. The inclusion in this table of any shares deemed beneficially owned does not constitute an admission of beneficial ownership of those shares.

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CORPORATE GOVERNANCE

Our Board believes that good corporate governance is important to ensure that NxStage is managed for the long-term benefit of our stockholders. This section describes key corporate governance guidelines and practices that we have adopted. Complete copies of our Corporate Governance Guidelines, Code of Business Conduct and Ethics, and committee charters, described below, are available under the Investor Relations — Corporate Governance section of our website at www.nxstage.com . Alternatively, you can request a copy of these documents by writing to Investor Relations, NxStage Medical, Inc., 350 Merrimack Street, Lawrence, Massachusetts 01843.

Corporate Governance Guidelines

Our Board has adopted Corporate Governance Guidelines to assist it in the exercise of its duties and responsibilities and to serve the best interests of NxStage and our stockholders. These guidelines, which provide a framework for the conduct of our Board, include the following provisions:

Board Leadership Structure

We separate the roles of Chief Executive Officer and Chairman of our Board in recognition of the differences between the two roles. Our Chief Executive Officer is responsible for managing our operations and, together with our Board, for setting our strategic direction, while our Chairman leads our Board in providing advice to and independent oversight of management. Separating these positions allows our Chief Executive Officer to focus on our day-to-day leadership and performance instead of Board administration. We believe this improves our Board’s ability to supervise and evaluate our Chief Executive Officer and other executive officers and enhances the independent and objective assessment of risk by our Board.

Risk Oversight

Our Board plays an active role, at both the Board and committee levels, in overseeing risk management. Our Board regularly reviews information provided by management regarding our liquidity, operations and compliance program, including conformity with our Code of Business Conduct and Ethics, as well as risks associated with each. Our Compensation Committee is responsible for overseeing the management of risks relating to our executive compensation plans and arrangements. Our Audit Committee oversees the management of risks relating to financial reporting, internal controls and information security. Our Nominating and Corporate Governance Committee oversees the management of risks associated with corporate governance, the independence of our Board and potential conflicts of interest. While each committee is responsible for evaluating certain risks and overseeing the management of such risks, the entire Board is regularly informed through committee reports about such risks.

Board Determination of Independence

Our Corporate Governance Guidelines provide that a majority of the members of our Board will be independent directors except as otherwise permitted by applicable NASDAQ rules. Our Board evaluates any relationship of each director with NxStage and makes an affirmative determination whether or not each director is independent. To assist it in making its independence determination, our Board has adopted independence standards in our Corporate Governance Guidelines, which incorporate the applicable provisions of our By-laws

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and the applicable rules and regulations of NASADQ and the Exchange Act. Further, our Board must consider whether each director has a relationship with NxStage that would interfere with the exercise of independent judgment in carrying out the responsibilities of a director. As part of our Board’s annual review of director independence, our Board considered the recommendation of our Nominating and Corporate Governance Committee and reviewed any transactions and relationships between each non-employee director or any member of his or her immediate family and NxStage.

Our Board has determined that each of our directors and nominees for director, other than Mr. Burbank, our Chief Executive Officer, is an independent director for purposes of serving on the Board and with respect to each director’s respective committee membership. Our Board made the same determination with respect to our former director Barry M. Straube at the time he was serving.

Communicating with Our Board

Our Board will give appropriate attention to written communications that are submitted by stockholders and other interested parties, and will respond if, and as, appropriate. The Chairman of our Board, with the assistance of our General Counsel, is primarily responsible for monitoring communications from stockholders and other interested parties and for providing copies or summaries to the other directors as he or she considers appropriate based on procedures approved by a majority of the independent directors. Under these procedures, communications will be forwarded to all directors if they relate to important substantive matters and include suggestions or comments that the Chairman of our Board considers to be important for the directors to know. In general, communications relating to corporate governance and corporate strategy are more likely to be forwarded than communications relating to ordinary business affairs, personal grievances and marketing matters.

Stockholders and interested parties who wish to send communications to our Board should address such communications to Board of Directors, c/o Winifred L. Swan, Secretary, NxStage Medical, Inc., 350 Merrimack Street, Lawrence, Massachusetts 01843.

Director Nomination Process

Our Nominating and Corporate Governance Committee is responsible for identifying individuals qualified to become directors, consistent with the criteria approved by our Board, and recommending individuals to be nominated for election as directors. The process followed by our Nominating and Corporate Governance Committee to identify and evaluate candidates may include requests to members of our Board and others for recommendations, the utilization of director search firms to help identify and recruit potential candidates, meetings from time to time to evaluate biographical information and background material relating to potential candidates, and interviews of selected candidates by members of our Nominating and Corporate Governance Committee and our Board. Mr. Peters and Ms. Donigan, who became directors in June 2016 and July 2016, respectively, were recommended as potential candidates by a director search firm.

In considering whether to recommend any candidate for inclusion in our Board’s slate of recommended director nominees, including candidates recommended by stockholders, our Nominating and Corporate Governance Committee applies the criteria that are set forth in our Corporate Governance Guidelines. These criteria include the candidate’s integrity, business acumen, knowledge of our business and industry, experience, diligence, conflicts of interest and the ability to act in the interests of all stockholders. Our Corporate Governance Guidelines specify that the value of diversity on our Board should be considered by our Nominating and Corporate Governance Committee in the director identification and nomination process. Our Nominating and Corporate Governance Committee seeks nominees with a broad diversity of experience, professions, skills, viewpoints and backgrounds. Our Nominating and Corporate Governance Committee does not assign specific weights to particular criteria and no particular criterion is a prerequisite for a nominee. The backgrounds and qualifications of our directors, considered as a group, should provide a significant mix of experience, knowledge and abilities that will allow our Board to fulfill its responsibilities. We believe that the current composition of our Board reflects such desired diversity in business and professional experience, skills and background.

Stockholders may recommend potential director candidates for consideration by our Nominating and Corporate Governance Committee by submitting the candidate’s name and appropriate biographical information,

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and, if the stockholder is not a stockholder of record, a statement as to whether the stockholder or group of stockholders making the recommendation has beneficially owned more than 5% of our common stock for at least a year as of the date such recommendation is made, to the Nominating and Corporate Governance Committee, c/o Winifred L. Swan, Secretary, NxStage Medical, Inc., 350 Merrimack Street, Lawrence, Massachusetts 01843. Assuming that appropriate biographical information has been provided on a timely basis, our Nominating and Corporate Governance Committee will evaluate stockholder-recommended candidates by following substantially the same process, and applying substantially the same criteria, as it follows for candidates submitted by others.

Our stockholders also have the right to nominate director candidates themselves, without any prior review or recommendation by our Nominating and Corporate Governance Committee or our Board, by following the procedures provided in our By-laws and described in the Other Matters — Stockholder Proposals for the 2018 Annual Meeting section of this proxy statement.

Committees and Meetings

Our Board has three standing committees, which are described in the table below. Each committee is governed by a written charter approved by our Board and posted on the Investor Relations — Corporate Governance section of our website, www.nxstage.com . Each member of our three standing committees is independent as defined under applicable NASDAQ rules, and each member of our Audit Committee satisfies the additional independence requirements under Rule 10A-3 of the Exchange Act.

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In 2016, our Board met 10 times and each of our current directors attended at least 75% of the total number of meetings of our Board and the committees on which he or she then served. Our Corporate Governance Guidelines provide that directors are expected to attend the annual meeting of stockholders. All of our then-serving directors attended our 2016 annual meeting of stockholders.

Code of Business Conduct and Ethics

We have adopted a written Code of Business Conduct and Ethics that applies to our directors, officers and employees, including our principal executive officer, principal financial and accounting officer and controller, or persons performing similar functions. We have posted a copy of the code on our website, www.nxstage.com . In addition, we will post on our website all disclosures that are required by law or NASDAQ rules concerning any amendments to, or waivers of, our code.