A postnuptial agreement, usually shortened to postnup, is a written agreement a married couple signs after the wedding, setting out how they would divide money, property and other assets if the marriage later ends. It works like a prenuptial agreement in almost every respect except one: timing. The prenup is signed before you marry, the postnup after, and that single difference in date is the only structural distinction English and Welsh law draws between them.
The legal test is the same one either way. Since the Supreme Court decided Radmacher v Granatino [2010] UKSC 42, a court will usually hold both partners to what they agreed, whether the document was signed before or after the wedding, provided it meets the same four conditions: full and frank financial disclosure, independent legal advice for each of you, no duress or undue pressure, and an outcome that is fair when the marriage actually ends. Postnups have their own supporting case law too. In MacLeod v MacLeod [2008] UKPC 64, the Privy Council held that postnuptial agreements are no longer against public policy in England and Wales, clearing the way for the approach Radmacher later confirmed for both types of agreement together. Source: Counsel Magazine, "The Rise of the Post-Nup".
If you are reading this because you are already married and never signed a prenup, or because your circumstances have changed since you did, this is the document that applies to you now. The rest of this article covers how a postnup differs from a prenup in practice, the situations that typically prompt one, and whether signing after the wedding changes your legal position for better or worse.
Postnup versus prenup: what actually changes
Structurally, very little. Both documents cover the same ground: what each of you owns going into the arrangement, how you will treat assets acquired during the marriage, and what happens to all of it if you divorce. Both are judged against the same Radmacher conditions. Neither is automatically binding in the strict contract-law sense; both are given decisive weight by a Family Court when properly done.
What changes is the starting point. When you sign a prenup, you are agreeing on paper what you intend before you have lived any of it out. When you sign a postnup, you are usually agreeing on paper what has already started to happen, or reacting to something that has already happened: an inheritance has landed, a business has been started, one of you has already given up work. The agreement is less speculative and more descriptive of a real situation, which can work in your favour when a court later asks whether you both understood what you were agreeing to.
| Prenup | Postnup |
|---|
| Signed | Before the wedding | After the wedding |
| Governing test | Radmacher v Granatino [2010] UKSC 42 | Same test, supported by MacLeod v MacLeod [2008] UKPC 64 |
| Typical trigger | Assets brought into the marriage | Assets or circumstances that changed during the marriage |
| Biggest risk to its weight | Duress from a looming wedding date | Fairness, given the marriage's real track record |
Do the four Radmacher conditions apply the same way?
Broadly yes, but two of them play out differently once you are already married.
Disclosure and legal advice work identically. Each of you still needs to lay out what you own and owe in full, and each of you still needs your own solicitor advising only you. Marriage does not relax either requirement. If anything, couples who have already been managing shared finances for a while often find full disclosure easier, because there is less to reconstruct from memory than there would be starting from scratch.
Duress is usually easier to avoid, structurally. The classic prenup risk, signing days before the wedding because the venue is booked and the guests are arriving, does not exist for a postnup. There is no ceremony bearing down on the signing date. That does not mean a postnup can never be signed under pressure: one partner threatening to leave, or making the agreement a condition of staying, is still duress, and a court will look at it the same way it would look at a rushed prenup. Timing simply removes the single most common source of pressure that trips prenups up.
Fairness at the time of divorce, the fourth condition, can cut the other way. By the time you sign a postnup, the marriage has a track record: years lived together, a career one of you may have paused, children who may already exist. A postnup that ring-fences one partner's assets without accounting for what the other partner has already contributed, financially or otherwise, is arguably more exposed to a fairness challenge than a prenup signed before any of that history existed, because the court is not imagining a hypothetical future, it is looking at a marriage that has already happened.
None of this makes a postnup weaker than a prenup as a category. It means the fairness condition deserves particular attention if you are drafting one partway through a marriage that has already changed both of your financial positions.
Why couples sign one
A postnup usually responds to something specific rather than being a routine step taken for its own sake. The situations that come up most often, according to family law solicitors who handle these agreements, include:
An inheritance received during the marriage. Money or property one of you inherits after the wedding is not automatically excluded from what a court could divide on divorce. A postnup can ring-fence it in writing, the same way a prenup ring-fences pre-marriage assets.
A business started or expanded after the wedding. If one of you launches a company, or a business you already had grows significantly, during the marriage, a postnup can set out how that business would be treated on divorce before its value becomes a point of dispute.
Reconciliation after a separation. "Following a temporary separation, couples who reconcile may wish to put a financial agreement in place as part of rebuilding their relationship," rather than as a step toward divorce.
One partner giving up a career to care for children. A postnup drafted at that point can address the new financial reality directly, reflecting that one partner's earning capacity has changed since the wedding, rather than simply ring-fencing what existed before children arrived.
Source for all four: WHN Solicitors, "What Is a Postnuptial Agreement? UK Guide"; business and inheritance triggers corroborated by Rayden Solicitors, "Postnuptial Agreement Solicitors UK".
A fifth, less discussed use: a postnup can also formally reaffirm or amend a prenuptial agreement once the marriage is underway, if circumstances have become clearer than they were on the wedding day.
Scotland is not covered by this
Postnuptial agreements in Scotland are dealt with under the same statute as prenups: section 16 of the Family Law (Scotland) Act 1985. Scottish law treats agreements as contracts a court is reluctant to unpick, testing fairness at the point of signing rather than at the point of divorce. If either of you has Scottish ties, do not assume the England and Wales approach above applies. See are prenups legally binding in the UK for the fuller Scotland comparison; the same distinction applies whether the agreement is signed before or after the wedding.
The couple this fits best
If the two of you are already married, your finances have likely already started to mix in ways a prenup never has to account for: a joint account, a mortgage in both names, a habit of covering each other's bills. That is exactly the position eziduo is built for. eziduo gives a couple a shared, ongoing forecast of income, spending and savings across the next twelve months, useful groundwork whether or not you end up signing a postnup. Sorting out what you each actually own, owe and contribute is the same exercise a postnup's disclosure condition demands. Couples who already track that together tend to find the disclosure stage far less painful than those starting from a blank spreadsheet under deadline.
Ana and Rafael, three years in
Ana and Rafael married without a prenup. Two years later, Rafael's father died and left him a share in the family's small property business, worth considerably more than anything either of them owned when they married. Ana had also stepped back from full-time work the year before, after their first child was born, and was earning less than half of what she had previously.
They decide a postnup makes sense: Rafael keeps the inherited business share separately, and Ana receives a larger proportion of any assets built jointly during the marriage than a simple fifty-fifty split, reflecting that her reduced income was a direct result of choices they made together as a couple.
They do this properly. Each instructs a separate solicitor. They exchange full statements, including the business valuation and Rafael's actual income from it. They sign with no pressure, on a quiet weekend with nothing else riding on the date. If they divorced years later, a court would very likely uphold this: disclosure was complete, advice was independent, there was no duress, and the terms account for what actually happened in the marriage rather than ignoring it. That last point is what would have been missing if they had simply copied a template clause ring-fencing "all assets acquired by either party" without adjusting for Ana's reduced earning capacity.
Common mistakes
Assuming a postnup needs no legal advice because you are already married and trust each other. The same independent legal advice condition applies. Trust is not the legal test; documented, independent advice is. See are prenups legally binding in the UK for the full four-condition test that applies to both prenups and postnups.
Treating a postnup as risk-free because there is no wedding date to rush you. It removes one source of duress risk, not all of them. Pressure from a partner threatening to end the marriage unless you sign is still duress.
Ring-fencing assets without accounting for what has already happened in the marriage. A postnup that ignores a career already paused, or years of joint contribution, is more exposed to a fairness challenge than a prenup signed with a blank slate.
Writing terms about children into the agreement. The same limits apply as for a prenup. See what cannot be included in a prenup in the UK for the full list of what a court will not enforce, in either document.
Waiting for a crisis to consider one. A postnup does not have to follow a separation. Couples who sign one calmly, after an inheritance or a career change, with time to think, are in a stronger position than couples drafting one during a difficult patch.
Where this leaves you
A postnuptial agreement is not a weaker or more desperate version of a prenup. It is the same legal tool, judged by the same test, used at a different point in the relationship, usually because something specific has changed: money has arrived, a business has started, or one of you has taken on more of the unpaid work of running a household and raising children. Signed properly, with disclosure, independent advice, no pressure and a fair outcome, it carries the same weight a prenup would.
As of today, this is the settled legal position for both types of agreement. It may not stay settled indefinitely. The Ministry of Justice ran a consultation called "A fairer end to relationships" from 5 June to 14 August 2026, proposing a new category of "qualifying nuptial agreements" that would be treated as more firmly binding than the current Radmacher approach allows. The consultation has closed. The government's response, and any resulting change to the law, is not yet known, and could still be years away even if it goes ahead. Nothing about the current test changes until it does.
This article is informational and does not replace independent legal advice from a solicitor. eziduo is not a law firm and does not provide legal advice. Given that independent legal advice is one of the conditions that gives a postnuptial agreement its weight, speaking to a solicitor before you sign anything is not optional.
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