Postnuptial agreements: making a marriage-era agreement stick

REVIEWED BY: Sean McNamara on 2026-08-31

What a postnup is

A postnuptial agreement is a written agreement made during a marriage or civil partnership setting out how assets, income and property will be divided if the relationship ends. It is the same idea as a prenup (see our prenup guide) but made after the wedding — often after a crisis, a business change, an inheritance, or a first separation-and-reconciliation. Cohabitation couples (who have no such status under English law) use the equivalent cohabitation agreement — see our cohabitation guide.

Are they binding?

No family agreement is automatically binding in England and Wales, but the Supreme Court in Radmacher v Granatino (2010) established the test the courts apply to both pre- and post-nups: the agreement will be given effect if it is fair, and both parties entered it freely, with full understanding. A properly drafted postnup, where both parties had independent legal advice and full financial disclosure, is very likely to shape — and often to control — the final outcome.

Key conditions for weight:

1. Informed, voluntary entry — no pressure, no "sign or else at the hospital". 2. Full and frank disclosure of both parties' assets and income. 3. Independent legal advice for each party — one lawyer cannot act for both. 4. Fairness on review — needs of both parties and any children must be met. 5. Properly drafted and executed as a deed, with a review clause for changed circumstances (children, illness, business failure).

When a postnup makes sense

After a reconciliation following separation — the agreement records what you agreed while tempers were factual rather than furious.
Significant inheritance or gift received during the marriage you want ring-fenced.
A business where a co-owner demands clarity about spousal claims.
A prior prenup that needs updating as circumstances changed.
Second marriages where each party wants their children's inheritance protected.

Limits

You cannot contract out of child maintenance or child-related court jurisdiction — arrangements for children are always subject to the child's welfare (see our child maintenance guides).
Undisclosed assets can unravel the agreement.
If circumstances change drastically (one party becomes disabled; children arrive with needs not anticipated), a court can depart from the deal because needs trump bargains.
Landmark fairness caveats still apply where one party would be left with needs unmet.

Cost-benefit reality

A well-drafted postnup costs a fraction of contested financial remedy proceedings. The worst postnup is a DIY template signed without disclosure or advice: it will be attacked successfully exactly when you need it. Budget for two solicitors, full disclosure schedules, and deed execution. If you are already separating, a postnup is the wrong tool — you want a separation agreement or a consent order (see our consent-order guide), which in financial remedy proceedings becomes binding.

prenup-agreements · consent-order · clean-break-orders · financial-remedy-guide · cohabitation-rights · form-e-disclosure

Official links

https://www.gov.uk/prenuptial-agreements (gov.uk overview page)
https://www.gov.uk/options-if-your-marriage-or-partnership-has-ended
https://www.lawsociety.org.uk (find a family-law solicitor)

This page is general information, not legal advice. YourFamilyCase.co.uk is an independent information directory and is not affiliated with HMCTS or gov.uk.

Content verified against the official HMCTS court directory, gov.uk forms and fees pages, and the professional body registers (SRA, FMC, Bar Council). Last reviewed September 2026.