What Is a Postnuptial Agreement? A UK Guide for Couples

You’re already married. Maybe you didn’t get round to a prenup before the wedding. Or something has changed—an inheritance, a business, children, or you’ve been through a rough patch and want to put your intentions in writing. A postnuptial agreement is the same idea as a prenup, but made after you’ve tied the knot. It doesn’t mean you’re planning to split; it means you’re being clear about what you’d both want if life took a different turn.

This guide explains what a postnuptial agreement is in the UK, when it makes sense, what you can include, how it differs from a prenup, and how to get one. It’s for couples who are already married or in a civil partnership and want to understand their options.

What is a postnuptial agreement?

A postnuptial agreement (often called a postnup) is a written contract made after you have already married or entered a civil partnership. Like a prenup, it sets out how you and your partner would divide money, property, and other assets if you later separate or divorce. The main difference is timing: a prenup is signed before the wedding; a postnup is signed once you’re already married.

In England and Wales, postnups are not fully binding in law—courts can take them into account but are not obliged to follow them. The same principles that apply to prenups (independent legal advice, full disclosure, no pressure) apply to postnups; courts will look at whether the agreement was fair and properly entered into. In Scotland, postnuptial agreements have been legally recognised for longer and are generally upheld if they’re fair and properly made. Northern Ireland has its own rules. In all cases, the aim is to give you both clarity and to reduce conflict and cost if the relationship ever ends.

People often turn to a postnup when they didn’t sign a prenup in time, when circumstances have changed since the wedding, or when they want to update or record their intentions after a period of difficulty or reconciliation.

When does a postnup make sense?

There’s no single rule. It often makes sense when:

You didn’t get a prenup — You married without an agreement and now want to record what you’d both agree should happen to your assets on divorce. A postnup can give you the same clarity as a prenup, after the fact.
Circumstances have changed — One of you has received or expects a large inheritance, started or grown a business, or had a big change in income or assets. You want to agree how that would be treated if you ever split.
There are now children (or stepchildren) — You want to clarify how assets would be shared or protected for children, or how stepchildren would be provided for. Courts will still prioritise the welfare of any children; the postnup can record your intentions.
You’ve reconciled after a separation — Some couples go through a difficult period and decide to stay together. They use a postnup to set out how they’d handle finances if they separated again, so both feel more secure.
You’re updating an existing agreement — You had a prenup (or an older postnup) and your situation has changed. A new postnup can replace or supplement it.

Not every couple needs one. If you’re both comfortable with the default rules that apply on divorce in your part of the UK and don’t have significant assets or changed circumstances, you might decide a postnup isn’t necessary. The key is that it’s a choice you make together, with no pressure and with proper advice.

What you can include in a postnup

Postnups in the UK typically cover the same areas as prenups:

Property — What happens to the family home, other properties, and how equity or sale proceeds would be split.
Savings and investments — What counts as matrimonial (built up during the marriage) vs separate (e.g. pre-marriage savings or inheritance), and how they’d be divided.
Pensions — Whether and how pension pots would be shared or offset. The agreement can record your intentions; courts have wide powers over pension sharing.
Debts — How existing or future debts would be allocated so one person isn’t left liable for the other’s borrowing.
Business assets — If one of you owns or part-owns a business, how that would be treated (e.g. kept separate, or valued and offset against other assets).
Maintenance — Whether either of you would pay the other spousal maintenance, and for how long. In England and Wales, courts can still order maintenance; the postnup can record what you’ve agreed as a starting point.

As with prenups, you cannot use a postnup to override the court’s duty to consider the welfare of any children, or to leave one of you in a position the court considers manifestly unfair. Full disclosure of your finances and independent legal advice for you both are essential—they make the agreement more likely to be upheld and show that it was entered into fairly.

How a postnup differs from a prenup

Timing — A prenuptial agreement is made before you marry or form a civil partnership. A postnuptial agreement is made after you’re already married or in a civil partnership. The legal idea is the same; the moment you sign is different.
Why choose a postnup — You might choose a postnup because you didn’t get a prenup in time, because you weren’t sure before the wedding, or because something has changed since you married and you want to record your current intentions.
How courts treat them — In England and Wales, courts consider both prenups and postnups in a similar way: they look at whether the agreement was entered into fairly (with advice, disclosure, and no duress). In Scotland, both are generally upheld if properly made. Your solicitor can explain how the courts in your area treat postnups specifically—in some cases the fact that you were already married when you signed can be a factor, but the principles of fairness and proper process still apply.

If you’re not yet married and are thinking about an agreement, a prenup is usually the right step. If you’re already married and want to put something in writing now, a postnup is the option.

How to get a postnuptial agreement in the UK

Talk about it together — Agree that you both want to explore a postnup. There’s no “right” moment, but it should feel like a joint decision, not one person pushing. If talking about money has been difficult before, this is a chance to do it with a clear purpose: What would we want to happen to our assets if we ever split?
List what you want to cover — Use the sections above as a starting point: property, savings, pensions, debts, business, maintenance. You don’t have to agree every detail yourselves; solicitors can help you turn your intentions into clear wording.
Each of you gets independent legal advice — This is essential. You each need your own solicitor so that no one can later say they didn’t understand or were pressured. It also makes the agreement more likely to be upheld. Costs vary; get quotes. Some firms offer fixed fees for straightforward postnups.
Disclose your finances — Both of you should provide a full and honest picture of your assets, debts, and income. An agreement based on incomplete or inaccurate information is more likely to be challenged later.
Sign when you’re both ready — There’s no fixed deadline (unlike a prenup, where signing too close to the wedding can be an issue). The important thing is that neither of you feels under pressure. Your solicitors will advise on timing and process.
Keep it and review it — Store signed copies safely. If your circumstances change significantly again, review the agreement and consider updating it.

Laws differ in England and Wales, Scotland, and Northern Ireland. A solicitor in your jurisdiction can advise on what’s enforceable and what to include.

The bottom line

A postnuptial agreement is a written contract made after you marry (or enter a civil partnership) that sets out how you’d divide assets if you divorced. In the UK, its legal strength varies by jurisdiction—courts in England and Wales can take it into account; in Scotland it’s more firmly recognised—but in all cases it gives you both a clear, agreed starting point and can reduce conflict and cost if the relationship ever ends.

It often makes sense when you didn’t get a prenup, when circumstances have changed (inheritance, business, children), or when you’ve reconciled and want to record your intentions. Each of you should get independent legal advice, disclose your finances fully, and sign without pressure. You’re not planning for failure; you’re making sure you’re both on the same page.

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