A prenup fails for procedural reasons far more often than unfair ones. Rushed signing and incomplete disclosure kill more agreements than harsh terms ever do.
Prenuptial agreements do not usually fail because a court decides the terms were unfair. They fail because of how they were signed — too late, without disclosure, without independent advice, or under circumstances a judge later describes as pressure.
Which is oddly reassuring, because those are procedural problems, and procedural problems are entirely preventable if you start early enough.
What these agreements actually do
A prenuptial agreement is a contract signed before marriage setting out what happens to property, debts and support if the marriage ends. A postnuptial agreement is the same contract signed after the wedding.
Without one, division is decided by your state's default rules — community property or equitable distribution — applied by a judge who has never met you. A prenup replaces that default with terms you chose while you still liked each other.
Common purposes:
- Protecting premarital assets — a property, savings, investments built before the relationship
- Protecting a business — particularly where partners or investors need certainty that a divorce will not disrupt ownership
- Protecting children from a previous relationship — ensuring an inheritance reaches them
- Ring-fencing an expected inheritance — which can otherwise become marital through commingling
- Allocating debt — so one party's student loans or business borrowing stays theirs
- Defining spousal support — capping, waiving or structuring it in advance
- Simply avoiding a fight — often the real reason, and a good one
A prenup is a divorce settlement written by people who love each other
That is the honest framing, and it is why couples who negotiate one calmly usually find it strengthens rather than damages the relationship. The conversation is uncomfortable once. The alternative is having it later under the worst possible conditions.
What makes one enforceable
Requirements vary by state, and many US states have adopted a version of the Uniform Premarital Agreement Act. The consistent elements:
- In writing and signed
Oral agreements are worthless here. Many states require notarisation or witnesses. - Full and fair financial disclosure
Both parties disclose all assets, debts and income. This is the most common failure point — an undisclosed account or an undervalued business can void the whole agreement. - Voluntary, without coercion
Signed freely, understanding what is being given up. - Independent legal advice for both
Not strictly required everywhere, and functionally essential. One lawyer cannot advise both parties. - Adequate time before the wedding
An agreement presented days before the ceremony invites a duress argument. Months, not days. - Not unconscionable
Terms leaving one party destitute while the other keeps everything can be struck down even where everything else was done correctly.
The timing rule that voids agreements
Signing the night before the wedding, or at the rehearsal dinner, is the single most reliable way to have a prenup thrown out. By then the other party cannot realistically refuse — guests have travelled, deposits are paid — and courts recognise that as pressure. Start the conversation at least three to six months before the date.
What cannot go in one
Child custody and child support. These belong to the court and are decided on the child's best interests at the time. You cannot pre-agree them, and attempting to can undermine the rest of the agreement.
Anything encouraging divorce. Terms that appear to reward ending the marriage may be void as against public policy.
Lifestyle clauses. Weight limits, frequency of intimacy, chore allocation, in-law visits. These appear in internet templates, are generally unenforceable, and make an otherwise sound agreement look unserious to a judge.
Anything illegal. Obviously, and it happens more than you would think in DIY documents.
Postnuptial agreements
Same contract, signed after the wedding, and courts scrutinise them more closely — because spouses owe each other fiduciary duties that engaged couples do not, and the leverage dynamic is different.
Common triggers:
- A prenup was intended but never finished before the wedding
- One spouse starts a business, or takes on investors who want certainty
- A substantial inheritance is received
- One spouse leaves work to raise children and wants protection for that decision
- Reconciliation after a separation, with terms agreed as part of it
- Significant debt is taken on by one spouse
That fourth one is worth emphasising, because postnups are often assumed to protect the wealthier spouse. A properly drafted postnup is frequently the strongest protection available to the spouse who gave up earning capacity to raise a family.
Where these agreements come apart
Hidden assets. The most common reason. If disclosure was incomplete, the agreement is vulnerable years later.
No separate lawyer. One lawyer drafting for both is a straightforward attack.
Signed under time pressure. As above.
The agreement was never updated. Terms fair for a couple with no children and modest assets can look very different after twenty years, three children and a career sacrifice. Some agreements include sunset clauses or scheduled reviews for exactly this reason.
Commingling defeated the intent. An agreement protecting a premarital property does not help much if the property was sold and the proceeds went into a joint account used for family expenses. Keep separate property genuinely separate.
Keep the paperwork trail
Store the signed agreement with the disclosure schedules, correspondence showing when it was first raised, and evidence that each party had their own lawyer. The document alone is not the case — the circumstances of signing are, and they are proved by the file, sometimes twenty years later.
What it costs
A straightforward prenup between two people with ordinary finances and no dispute typically runs from a low four-figure sum per side. Complex agreements involving business valuations, trusts or international assets cost considerably more.
Set against a contested divorce, where five figures per side is routine, the arithmetic is not close — provided the agreement is properly made. A badly made one is worse than none, because it creates litigation about the agreement in addition to litigation about the divorce.
This is a field where DIY templates are genuinely dangerous. The document is not the value; the disclosure process, the independent advice and the timing are.
The UK position
Prenuptial agreements are not automatically binding in England and Wales. Courts retain discretion over financial provision.
However, following the Supreme Court's decision in Radmacher, courts give effect to a nuptial agreement freely entered into by parties with a full appreciation of its implications, unless it would be unfair to hold them to it. In practice, a well-made agreement is highly persuasive.
The Law Commission has recommended making qualifying agreements binding subject to safeguards, though that has not been enacted.
What makes a UK agreement persuasive:
- Signed well in advance — at least 28 days before the wedding is the commonly cited minimum, and more is better
- Full financial disclosure by both parties
- Independent legal advice for each
- No pressure or undue influence
- Terms that meet both parties' needs, particularly any children's
- Reviewed after major life events
That last requirement is the practical one that catches people. An agreement leaving one spouse and the children without adequate provision will not be upheld regardless of how carefully it was signed — English courts will not allow a party to be left in real need.
Who genuinely needs one
Prenups are associated with wealth, and that association means the people who benefit most often do not consider one.
Business owners. The clearest case. Without an agreement, growth in the business's value during the marriage may be marital property, and a divorce can force a valuation, a buyout, or in the worst case disruption to the company itself. Partners and investors increasingly ask whether founders have one.
Second marriages with children. Without an agreement, assets intended for children from a first marriage can pass to a surviving spouse and then out of the family entirely. This is the situation where the absence of a prenup causes the most lasting damage.
People with significant debt. Protecting your spouse from your student loans or business borrowing is as legitimate a use as protecting assets, and it makes the agreement mutual rather than defensive.
Anyone expecting an inheritance. Inheritances are generally separate property, and generally lose that status through commingling. An agreement plus disciplined account separation is what actually preserves it.
A spouse leaving work to raise children. The most under-recognised case. An agreement can guarantee support terms recognising a career sacrifice that would otherwise be argued about later.
International couples. Where one spouse holds assets abroad or you may live in different countries, which law applies becomes a live question. Agreements here need advice in each relevant jurisdiction.
How to raise it without damaging the relationship
The conversation is the hard part, and the timing of it matters more than the wording.
Raise it early — around engagement, not around invitations. Late raising is what feels like an ambush.
Frame it as planning, not distrust. Couples make joint decisions about insurance, wills and mortgages without treating them as predictions of disaster. This is the same category.
Be honest about who is asking and why. If parents or business partners are driving it, say so rather than presenting it as your own idea.
Make it mutual. An agreement protecting only one side reads as one-sided and is more vulnerable legally as well as emotionally.
Let each of you have your own lawyer from the start. It is a legal requirement in practice and it also removes the sense that one person is being managed.
The summary
Start at least three to six months before the wedding. Disclose everything, in writing, with schedules attached. Each of you gets your own lawyer. Leave out custody, support for children and lifestyle clauses. Keep separate property genuinely separate afterwards. Review it after major life changes.
Do those things and you have an agreement that is likely to be upheld. Skip any of them and you have an expensive document that gives your future selves something extra to argue about.
Frequently asked questions
Are prenuptial agreements enforceable?
In most US states yes, if there was full financial disclosure, independent legal advice for both parties, no coercion, and adequate time before the wedding. In England and Wales they are highly persuasive rather than automatically binding.
What is a postnuptial agreement?
The same contract, signed after marriage. Common when finances change significantly — an inheritance, a business sale, or as part of reconciling after a separation.
What cannot go in a prenup?
Child custody and child support terms cannot be pre-decided, because those belong to the court and the child's interests. Non-financial lifestyle clauses are generally unenforceable too.