A prenuptial agreement can give couples greater clarity about their finances before marriage. It can record how they intend to deal with property, savings, pensions, business interests and inherited wealth if the relationship ends. For couples with substantial assets or children from an earlier relationship, that certainty can be particularly valuable.

However, an agreement signed before a wedding may be examined many years later, when the couple's finances, responsibilities and needs look very different. Questions can also arise about whether both people understood the terms or had all the information they needed before signing.

This article explains when the courts in England and Wales may depart from a prenuptial agreement, what makes a challenge more persuasive and how to assess your position if a prenup is disputed.

Why are prenups not legally binding in the UK?

In England and Wales, a prenuptial agreement does not remove the family court's power to decide a fair financial settlement when a marriage breaks down. Under the Matrimonial Causes Act 1973, the court considers matters including income, assets, financial needs, earning capacity and the welfare of children. Comparable principles apply to the financial consequences of civil partnership dissolution.

The leading authority is the Supreme Court's 2010 decision in Radmacher v Granatino. The court established that a nuptial agreement should generally be given effect where each party entered into it freely, fully appreciated its implications and it would be fair to hold them to it in the circumstances prevailing at divorce.

This gives properly prepared nuptial agreements considerable, and potentially decisive, weight. It does not mean every agreement will be enforced or that a judge must accept every provision.

The Law Commission recommended reforms in 2014 to introduce qualifying nuptial agreements. In 2026, the government consulted on introducing binding qualifying nuptial agreements in England and Wales. However, these remain proposals rather than the rules currently governing prenups.

For couples preparing an agreement, our prenuptial agreement solicitors can explain the safeguards that strengthen its position if it is later scrutinised.

What can invalidate a prenuptial agreement?

There is no single checklist that automatically voids a prenup. A court examines both how an agreement was made and whether its terms should be followed when the couple divorces. These are different questions: an agreement may be undermined by problems at signing, or the court may give it less weight because of the outcome it would now produce.

One party was pressured into signing

A prenuptial agreement should be freely entered into. Evidence of duress, coercion or undue influence can raise serious questions about whether one spouse genuinely agreed to its terms.

For example, one partner might present a substantially revised agreement immediately before the wedding and threaten to cancel the ceremony unless it is signed. The court would examine what happened, how much time was available and whether the person could make an informed choice.

The general recommendation is that a prenup should be completed and signed well before the wedding, ideally at least 28 days beforehand. However, there is no universal statutory 21-day or 28-day rule that automatically makes an agreement invalid if it is signed later. The surrounding circumstances matter more than a fixed number of days.

One party did not fully disclose their finances

Both parties should have an accurate picture of the other's financial circumstances before agreeing how assets will be divided. Full financial disclosure typically covers property, savings, pensions, investments, debts, income and business interests.

If one spouse deliberately conceals a significant amount of wealth, the other may not have understood what they were agreeing to. Inadequate disclosure can therefore be a powerful reason to question the validity of the agreement, particularly where the parties expressly agreed to fully disclose their finances.

Not every omission has the same implications. The court will consider its significance, whether the missing information affected the decision to sign and what the parties knew at the time.

One party did not understand the agreement

Both people should understand the legal and financial consequences of signing a prenup. Independent legal advice is a key safeguard because each person has the opportunity to discuss the terms with a family lawyer acting solely in their interests.

If one party signed without receiving independent legal advice, that may raise questions about whether they had a full appreciation of the agreement's implications. This could be especially important where the terms were complex, involved overseas assets or contained substantial restrictions on future financial claims.

The absence of advice does not automatically mean an agreement will be disregarded. Equally, the fact that both parties received independent legal advice does not guarantee that every term of the agreement will be upheld. The court looks at the full picture, including what each person actually understood.

An agreement may also be questioned if a person's capacity to understand or freely agree to its terms was materially affected at the time of signing. A mental health diagnosis alone is not evidence that a person lacked capacity or could not consent.

The agreement would leave one spouse with unmet financial needs

The court may decline to follow a prenup where doing so would leave one spouse unable to meet reasonable financial needs. This can include housing, income and, where relevant, provision for children.

For example, an agreement might state that one spouse keeps the family home and all business assets, while the other receives no capital or spousal maintenance. If the latter has limited earning capacity after years spent caring for children, following those terms may be unfair.

An agreement is not necessarily invalid simply because one party receives less than they might have received without it. The central question is whether giving effect to its terms would be fair in the circumstances.

Circumstances have changed significantly since signing

A prenup may have been reasonable when it was signed but no longer reflect the couple's needs years later. Children, illness, reduced earning capacity, substantial changes in wealth or financial dependence can all affect the fairness assessment.

For instance, one partner may have expected to remain in full-time employment but later stopped working to care for children. A financial arrangement made before that decision might not make adequate provision if the marriage ends.

A change in circumstances does not automatically cancel the original agreement. The court considers how significant the change is and whether it would now be unfair to hold the parties to their earlier intentions.

The agreement contains terms the court cannot uphold

Prenuptial agreements are primarily concerned with financial matters. They cannot conclusively determine where children will live, how much time they will spend with each parent or remove the legal framework governing child maintenance. Children's welfare and applicable maintenance rules take priority.

Provisions intended to control personal behaviour, or to impose a financial penalty simply because one partner has been unfaithful, should not be assumed to be enforceable. However, an inappropriate clause does not necessarily mean every other provision must be disregarded.

For a fuller explanation, read our guide to what cannot be included in a prenup.

JMW case study: can a prenup be overturned because of financial non-disclosure?

Financial non-disclosure was central to the Court of Appeal's 2025 decision in Entwistle v Helliwell, a case in which I acted for the husband.

The couple had signed a prenuptial agreement on their wedding day. The wife disclosed assets worth approximately £18 million, although her wealth at the time was substantially greater, in the region of £60 million to £70 million. The agreement sought to provide that each spouse would retain their own assets if the marriage ended.

At the original financial hearing, the judge gave the agreement substantial weight. The husband appealed. The Court of Appeal concluded that the wife had deliberately failed to disclose the true extent of her assets and that the agreement should not be upheld. The husband's financial needs had to be reconsidered without treating the prenup as controlling the outcome.

The case demonstrates that material non-disclosure can have serious consequences even where an agreement has been signed. It does not establish that every missing financial detail will invalidate a prenup; the extent of the omission and the circumstances are important.

You can read JMW's analysis of Entwistle v Helliwell and the dangers of non-disclosure for more detail.

How easy is it to overturn a prenup?

A prenup is not easy to overturn simply because one spouse no longer likes its terms. An agreement that was carefully prepared, freely entered into and remains fair can carry decisive weight in financial remedy proceedings.

Factors that generally make an agreement more likely to be respected include:

• Both parties sought independent legal advice before signing.
• Each person provided sufficiently detailed and accurate financial disclosure.
• There was enough time to consider, discuss and negotiate the terms without undue pressure.
• Both people understood the implications, including rights they might otherwise have on divorce.
• The agreement makes fair provision for the parties' reasonable financial needs and those of their children.

A challenge is therefore strongest when it identifies a substantive problem supported by evidence. Disagreement over the division of matrimonial property, or a belief that one spouse secured a better bargain, will not necessarily justify departing from the agreement.

Nor does adultery usually provide a route around a prenup. Divorce in England and Wales is now based on a no-fault process, and infidelity will not usually determine a financial settlement. The court's focus is on the financial and legal factors relevant to fairness.

What happens if circumstances change after signing a prenup?

Not every change means a prenup should be set aside. A rise in one spouse's salary, a new investment or a change in property values may already have been anticipated by the agreement. The important question is whether the terms still produce a fair result when the court is asked to consider them.

The position may be different if one partner has become dependent on the other, or if children and caring responsibilities have created needs the original document did not address. This is why couples may benefit from reviewing their arrangements during marriage, rather than waiting until separation.

If both spouses agree, they can use a postnuptial agreement to reaffirm, amend or replace an earlier prenup. A postnuptial agreement is entered into after marriage and should be supported by appropriate disclosure and independent legal advice. It is not a unilateral way for one spouse to legally amend the original agreement.

Our guides explain what a postnuptial agreement is and how couples can put an agreement in place after marriage.

What should you do if you believe your prenup is unfair?

If you are concerned about an agreement you signed, start by establishing why its terms may be open to challenge. You do not need to decide for yourself whether the whole agreement is invalid before seeking advice.

Practical steps include:

1. Review the signed agreement. Check its terms, any review clauses and the financial assumptions on which it was based.
2. Gather the documents from when it was made. Correspondence, draft agreements, financial schedules and records of legal advice may help establish what was disclosed and how the agreement was negotiated.
3. Identify what has changed. Consider current income, housing, pensions, business interests, childcare responsibilities and any additional financial needs.
4. Seek independent legal advice before agreeing to a settlement. A solicitor can assess the weight the court is likely to give the prenup and the available options for resolving a dispute.

An agreement can be challenged within financial remedy proceedings, but that does not mean a contested final hearing is inevitable. Depending on the circumstances, the parties may be able to negotiate an outcome that properly reflects their financial position.

JMW's solicitors for contesting prenuptial agreements advise on both challenging and defending existing agreements, including disputes involving business assets, inherited wealth and complex financial arrangements.