How to modify child support or alimony in New Hampshire

Sources last checked: 7 November 2026. Information only, not legal advice. The Cusp is not a law firm.

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The short version

New Hampshire sets different tests for the two kinds of order, and both come from the statutes. For child support, RSA 458-C:7 lets either parent ask for a change three years after the last support order “without the need to show a substantial change of circumstances”, and at any time with one. For alimony, RSA 458:19-aa is stricter: a contested change needs findings, “based on clear and convincing evidence”, of a substantial and unforeseeable change in circumstances, no undue hardship, and that justice requires a change. In both cases a change cannot start before the other person has been given notice of your petition.

Child support

Who and where: the obligor or obligee may apply to the court, or to the Department of Health and Human Services when the Department issued the order, “whichever issued the existing order”.
The three-year route: three years after the entry of the last support order, either parent may ask without proving a change in circumstances. The section adds that it does not stop anyone from applying “at any time for a modification based on substantial change of circumstances”. The statute does not define “substantial” or give a percentage test, and we read no court decision on it.
The state agency: the Department must give parties to orders it handles notice of their right to a review at least once every three years. For orders assigned to the Department, it must review them on the same schedule and, if appropriate, “apply for adjustment of the child support order”.
The result: a change is made “in accordance with the child support guidelines” where the Department seeks one. We did not read the guidelines sections of the chapter, so this page does not say how the new number is worked out.

Alimony

What can change: the court may modify the amount or duration of a term alimony order “upon agreement of the parties” or, without agreement, on one party’s petition or motion. The statute defines modification as “any increase or decrease in the amount or duration in alimony”, other than because of cohabitation, remarriage, death or retirement, which have their own rules.
The test when it is contested: the court must find all three of these, on clear and convincing evidence: “substantial and unforeseeable change of circumstances” since the effective date of the order, “There is no undue hardship on either party”, and “Justice requires a change in amount or duration”.
The burden: “The party requesting a modification shall have the burden of proof”. If the old order has ended, “reinstatement shall be requested within 5 years after the end of the order”.
Retirement: term alimony “shall end upon the payor reaching full retirement age or actual retirement”, whichever is later, unless the parties agree otherwise or the court finds special circumstances. The payor must give reasonable notice, and “Sixty days’ notice shall be presumed to be reasonable”. The court can extend alimony past retirement if justice requires.
Cohabitation: the court may modify or end alimony on a finding of a “relationship between an alimony payee and another unrelated adult resembling that of a marriage” that makes continuing the order unjust. The ordinary three-part test does not apply to that request. If alimony ended because of cohabitation or remarriage, reinstatement can be sought if “the request is made within 5 years” of the termination order.
Death: unless the court orders otherwise, “the obligation to pay alimony ends on the death of the payee”.
Older cases: these rules apply to modifications only for cases whose petition was filed on or after 1 January 2019, unless the court finds the original order adopted them. The statute says the provisions “shall not apply to modifications of orders in cases whose initial petition” was filed before that date. Older cases follow the law in effect when the petition was filed.
A closed window: the statute allowed a modification of a post-2018 order without the full findings only if the alimony exceeded 23 percent of the income difference and the petition was filed by 1 July 2022. That date has passed.

Timing: a change cannot reach back

Child support: a modification “shall not be effective prior to the date that notice of the petition” has been given. Notice means service as in civil actions, or acceptance of a copy of the petition if it is filed within 30 days and the petitioner provides “proof of acceptance by a certified mail receipt”.
Alimony: parties may agree to a retroactive change. If it is contested, the change “shall not be effective prior to the date that the notice of the petition” was given to the other party.
Overpayments: where a child support change creates an overpayment, the court shall order “the obligee to directly reimburse the obligor for such overpayment of support”, or adjust the new order until it is repaid, “absent a showing of undue hardship”. Only overpayments after notice count, and the reimbursement order takes effect 30 days after it issues unless a party asks for a hearing.

Before you file

Find the date your last support order was entered. That date decides whether the three-year route is open for child support.
Decide which kind of change you are asking for. A request to change alimony has a much higher bar than one to change child support, and the statute puts the burden of proof on the person asking.
Serve or give notice as early as you can. Because a change cannot start before notice, delay costs money for whoever expects the change.
If you are not sure which court or agency issued your order, check the order itself. Court staff cannot give legal advice. See legal aid in New Hampshire for free or low-cost help.

What we could not confirm

Court forms, fees and local practice. The New Hampshire Judicial Branch (www.courts.nh.gov) returned an Access Denied page (HTTP 403) to our robots.txt request on 7 November 2026, so under our crawling rules we read nothing from it. We cannot name a form, a filing fee, a fee waiver or a filing deadline.
The state child support agency’s own pages. http://www.dhhs.nh.gov also returned HTTP 403. We read the statute that describes the Department’s role, but not its application process.
How the new child support figure is calculated. We read RSA 458-C:7 only. We did not read the guidelines sections of the chapter, so we state no formula, threshold or income figure.
What “substantial” means in practice. The statutes use the word without defining it for child support. We read no court decision.
Whether the statutes have changed since our last check. The General Court’s pages show RSA 458-C:7 last amended in 2009 and RSA 458:19-aa in 2021, and we did not look for newer session laws.
Parenting time and custody. This page covers money only.

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