Prenup vs Postnup: What's the Difference and Do You Need One?
Neither a prenuptial nor a postnuptial agreement is automatically binding in England and Wales — but since a landmark 2010 Supreme Court case, courts have given both real weight when they're done properly. The main difference between them is simpler than people expect: timing.
The core difference: when it's signed
A prenuptial agreement ("prenup") is signed before the wedding. A postnuptial agreement ("postnup") is signed after the wedding — sometimes years into a marriage, often triggered by a specific event: one partner starting or selling a business, receiving an inheritance, or simply wanting to formalise an arrangement the couple never got round to before marrying.
| Prenuptial agreement | Postnuptial agreement |
|---|---|
| Signed before marriage | Signed during marriage |
| Common when one partner has significantly more assets, a business, or children from a previous relationship entering the marriage | Common after a windfall, inheritance, business sale, or to formalise financial arrangements once the marriage is underway |
| Best practice: signed at least 28 days before the wedding, to avoid any suggestion of pressure | No wedding deadline pressure — can be revisited any time the couple agrees |
Are they actually legally binding?
Neither type is automatically binding the way a commercial contract is — a court retains the power to depart from either if it would produce an unfair outcome, particularly around children's needs. But following Radmacher v Granatino [2010] UKSC 42, the Supreme Court held that courts should give an agreement "decisive weight" where it was freely entered into by each party with a full understanding of its implications, unless it would be unfair to hold them to it. MacLeod v MacLeod [2008] UKPC 64 separately confirmed postnuptial agreements can carry similar weight, and clarified that a prenup can't simply be varied by a later informal understanding — a proper postnup is needed for that.
What makes either more likely to be upheld
- Both parties received independent legal advice before signing
- Full and honest financial disclosure was given by both sides
- Neither party was under pressure or time constraints — for a prenup, signing well before the wedding (not the night before) matters
- The agreement doesn't leave either party, or any children, without reasonable provision for their needs
- Both parties genuinely understood what they were signing
Frequently asked questions
Are prenups legally binding in the UK?
Not automatically, but courts give them significant weight if entered into freely, with full disclosure and independent legal advice, and the outcome isn't unfair.
What's the difference between a prenup and a postnup?
Timing — a prenup is signed before marriage, a postnup during it. The legal principles for how much weight a court gives each are broadly the same.
Can we sign a postnup instead if we didn't do a prenup?
Yes — a postnup is a completely valid way to formalise financial arrangements at any point during a marriage, not just a fallback.
What makes a prenup more likely to be upheld by a court?
Independent legal advice for both parties, full financial disclosure, no pressure or rushed timing, and an outcome that doesn't leave either party or any children without reasonable provision.
Does this apply to civil partnerships?
Yes — the same principles apply to civil partnership agreements as to marriage.
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