A postnuptial agreement ("postnup") in the UK is simply a prenup made after you are already married. It does the same job — setting out how you would divide money and property if the marriage ended — and the courts treat it on much the same basis as a prenup. If you have already tied the knot, it is not too late to get the clarity and protection a prenup offers; a postnup is the tool for exactly that. This guide explains how postnups work, when couples make one, how much weight they carry and what they cost.
What is a postnuptial agreement?
A postnup is a written agreement between a married couple (or civil partners) recording what each of them owns, what should stay separate, what is shared, and how their finances would be divided if they separated. The only real difference from a prenuptial agreement is timing — a prenup is signed before the wedding, a postnup after it. For a side-by-side comparison, see prenup vs postnup.
Do postnups carry the same weight as prenups?
Broadly, yes. The leading case on agreements, Radmacher v Granatino (2010), applies to both prenuptial and postnuptial agreements: a court should give effect to an agreement freely entered into by each party with a full appreciation of its implications, unless in the circumstances it would not be fair to do so. As with a prenup, a postnup is not automatically binding, and the court keeps its duty to meet needs and provide for children. See are prenups legally binding? and are postnups legally binding?
Interestingly, a postnup can be viewed as entered into with fewer pressures than a prenup, because there is no wedding day bearing down on the decision — which can actually strengthen the argument that it was signed freely.
When do couples make a postnup?
There are a handful of common triggers:
- They meant to make a prenup but ran out of time before the wedding.
- Their finances have changed — an inheritance, a new business, a property purchase.
- One partner is giving up work to raise children and both want fair provision agreed.
- They are reconciling after a difficult patch and want clarity going forward.
- They already have a prenup and want to update it as life moves on.
See also making a postnup years into a marriage and how to get a postnup.
How a postnup is made
The same good practice that makes a prenup robust applies to a postnup:
- Full and frank financial disclosure from both partners.
- Independent legal advice for each of you.
- Fair terms that meet both partners' needs.
- The agreement executed as a deed, signed in front of an independent witness.
For what to cover, see what to include in a prenuptial agreement — the same list applies to a postnup.
Postnuptial agreements in the UK: are they worth it?
For many couples a postnuptial agreement in the UK is well worth it. It brings the same clarity and protection as a prenup — over property, savings, a business or an inheritance — but can be made at any point in the marriage, with no looming wedding date to create pressure. That calm timing can actually help, because it makes it easier to show the agreement was entered into freely. The cost is modest next to a contested divorce, and you can update the agreement again later if your circumstances change.
The statute knows a postnup by another name
Unlike a prenup, an agreement made after the wedding has a place in the legislation. Section 34 of the Matrimonial Causes Act 1973 defines a "maintenance agreement" as a written agreement between the parties to a marriage containing financial arrangements, made during the marriage or after it has ended, and a postnup is exactly that. Two consequences follow. Any term that tries to restrict the right to apply to the court for financial provision is void, though the rest of the agreement stands, so a postnup cannot oust the court any more than a prenup can. And under section 35 the court may alter the financial terms of the agreement if circumstances have changed or it fails to provide properly for a child, which gives a postnup a statutory route to being updated that a prenup lacks.
The test for weight is the one the Supreme Court laid down in Radmacher v Granatino, and it laid it down for post-nuptial agreements in the same breath as ante-nuptial ones: the court gives effect to an agreement freely entered into by each party with a full appreciation of its implications unless in the circumstances prevailing it would not be fair to hold the parties to it. "Freely entered into" is examined with particular care for a postnup made after a crisis in the marriage, because the partner who wants to stay married may sign under pressure the other partner is in a position to apply. Independent legal advice for each of you, and financial disclosure that reflects the position now rather than at the wedding, are the answer; the Law Commission treated both as requirements of a qualifying nuptial agreement.
When a postnup is the better tool
A postnup describes the marriage as it is rather than as it was expected to be, and that is its advantage. The Supreme Court's 2025 decision in Standish v Standish confirmed that the sharing principle applies to matrimonial property and not to assets brought into the marriage unless the couple have over time been treating them as shared; after ten years of marriage an accurate account of which assets have crossed that line is only possible with hindsight, and a postnup can give it. It is also the right instrument where a prenup is out of date, where an inheritance or a business has arrived since the wedding, or where a prenup was signed too close to the ceremony to be safe and the couple want to confirm it calmly afterwards. Executed as a deed under section 1 of the Law of Property (Miscellaneous Provisions) Act 1989, with each signature witnessed, it carries the same weight as the prenup it confirms or replaces.
Postnuptial agreement FAQs
Are postnuptial agreements legally binding in the UK?
Not automatically, but a fair postnup made with disclosure and advice is given significant weight (see are postnups binding?).
How much does a postnup cost?
Much the same as a prenup — from £199 online, or four figures via a solicitor (see postnup costs).
Can you get a postnup years after marriage?
Yes — you can make one at any stage of a marriage (see a postnup after years married).
Is a postnup as good as a prenup?
It is judged on the same principles and can be just as effective; the main thing is that it is fair and properly made (see prenup vs postnup).
Can a postnup be used to save a marriage?
Sometimes — agreeing finances can remove a source of conflict, and postnups are occasionally made during reconciliation (see a postnup after an affair).
Create your prenuptial agreement online
UK Prenup lets couples in England & Wales create a clear, fair prenuptial agreement online from £199, with your document generated instantly as a PDF. See how it works or get started.
UK Prenup is not a law firm and does not provide legal advice. A prenuptial agreement in England & Wales is not automatically binding, and both partners should take independent legal advice before signing.