Fairness is the heart of how courts treat prenups in England & Wales. Since Radmacher v Granatino, the rule is that a court will give effect to an agreement unless, in the circumstances, it would be unfair to hold the couple to it. So a court will follow a prenup that is fair, and decline to follow one that is not – which makes understanding what “unfair” means in practice the key to making an agreement that holds up.
This guide explains when fairness is judged, exactly what tips an agreement into “unfair” territory, and the practical steps that keep your prenup on the right side of the line.
When fairness is judged
Importantly, fairness is assessed at the time the court looks at the agreement – usually on divorce – not when it was signed. An agreement that seemed perfectly fair on the wedding day can become unfair if life turns out very differently: children arrive, a career is given up, an expected inheritance never comes, or one partner’s finances collapse. This forward-looking test is why a prenup needs to be built to last, and why a review clause matters so much (see also does a prenup expire?).
Two kinds of fairness: how it was made, and what it says
It helps to see that a court looks at fairness in two dimensions:
- Procedural fairness – how the agreement was made. Was there full disclosure? Did each partner have independent advice? Was it signed freely and in good time, free from pressure?
- Substantive fairness – what the agreement actually does. Does it meet both partners’ needs and provide for children, or does it leave one partner with nothing?
An agreement can fail on either count – a fair-looking deal made under pressure is as vulnerable as a freely made deal with cruel terms.
What makes a prenup unfair
- It would leave one partner in real need while the other keeps everything – the one line a prenup can never cross.
- It makes no provision for children, or ignores changes like the birth of a child.
- One partner did not give full financial disclosure.
- One partner had no independent legal advice and did not understand the agreement.
- It was signed under pressure or at the last minute.
- Circumstances have changed dramatically in a way the agreement never anticipated.
Any of these can lead a court to give the agreement reduced weight or, where several combine, to set it aside. In Ipekçi v McConnell (2019), for example, a mix of no disclosure, no effective advice and terms that would have left a partner in need meant the agreement was given no weight at all (see UK prenup court cases).
“Unfair” does not mean “unequal”
A common misconception is that a prenup must split everything down the middle to be fair. It does not. A court can and does uphold agreements that treat the partners very unequally – for example ring-fencing an inheritance or a pre-owned business – provided the outcome still meets the other partner’s reasonable needs. Fairness is about not leaving someone stranded, not about arithmetic equality. That distinction is what lets a prenup do useful work while staying enforceable (see matrimonial vs non-matrimonial property).
How to keep your prenup fair
Aim for an agreement that protects what genuinely needs protecting – premarital assets, a business, an inheritance – while still treating both partners decently and providing for any children. Do the groundwork that supports fairness:
- Exchange full financial disclosure.
- Take independent advice each.
- Sign in good time before the wedding.
- Provide a genuine floor for the weaker partner and room for children.
- Add a review clause so the agreement keeps pace with your lives.
A fair prenup is the kind a court will actually uphold – for the full method, see how to make a prenup fair and a prenup fair to both partners.
What the case law shows about fairness
The decided cases put flesh on the principle. In Ipekçi v McConnell an agreement was treated as unfair and given no weight because disclosure and advice were lacking and it would have left a partner in need. In Luckwell v Limata the court would not leave a father without a home while he cared for young children, despite the agreements he had signed. Yet in cases like Crossley v Crossley and Z v Z, where the couples were wealthy and the terms did not leave anyone stranded, the agreements were largely upheld. The pattern is consistent: unfairness is about leaving someone below the needs line or cutting corners in how the deal was made – not about the split being generous to one side (see UK prenup court cases).
The safety valve: how a change of circumstances bites
Because fairness is judged at the divorce, the most common way a once-fair prenup becomes unfair is simply the passage of life. The law does not expect a couple to predict the future, so it keeps a safety valve: if circumstances have changed in a way the agreement never contemplated, the court can decline to hold the couple to terms that no longer fit. The classic triggers are the arrival of children, one partner giving up a career to care for the family, a serious illness or disability, or an expected inheritance that never materialises. In each case the agreement is not being punished for being one-sided at the outset – it is being measured against a life that turned out differently. A shorter marriage gives less room for this drift, which is partly why prenups tend to be followed most closely in short, childless marriages; the longer the marriage and the more life has moved on, the more carefully a court will look.
Designing for fairness over time
The good news is that you can design an agreement to age well. A few features make a prenup much more likely to still look fair years later:
- A review clause. A commitment to revisit the terms on big life events – marriage milestones, children, a major change in wealth – keeps the agreement aligned with reality (see review clauses).
- Provision that scales. Terms that give the financially weaker partner more the longer the marriage lasts, or on the birth of a child, build fairness in from the start.
- A genuine floor. Guaranteeing housing and income for the weaker partner, rather than leaving them exposed, is the surest way to stay on the right side of the needs principle.
- Fair process, not just fair terms. Disclosure, advice and good timing protect the agreement even if the terms are later questioned.
An agreement built this way is not a fixed snapshot that dates the moment it is signed; it is a living arrangement that a court can comfortably uphold even after many years.
Fairness cuts both ways
It is easy to assume the fairness test only ever protects the poorer partner, but it works in both directions. A court is just as capable of holding a reluctant partner to an agreement they now regret as it is of relieving a partner from genuinely harsh terms. Where a couple were both wealthy, both advised, and the terms leave neither in need, the agreement is likely to be enforced even if one of them would now prefer a bigger share – as in cases like Crossley and Z v Z. Fairness is not a licence to escape a considered bargain simply because you could have done better; it is a guard against outcomes that leave someone stranded or that flowed from a flawed process. Understanding that balance is reassuring: a fair agreement, properly made, gives both partners real certainty (see a prenup fair to both partners).
When is a prenup unfair? The court’s view
A court treats a prenup as unfair, and declines to follow it, mainly when it would leave a partner or children in real need, was made without disclosure or advice, was signed under pressure, or no longer fits circumstances that have changed dramatically. Because fairness is judged at the time of the divorce, the safest agreements protect specific assets while still providing for both partners – and include a review clause to stay fair over time.
How the courts have drawn the line since Radmacher
The Supreme Court in Radmacher v Granatino named three situations in which holding a couple to their agreement is likely to be unfair: where it would leave one party in a predicament of real need while the other has plenty, where it fails to provide for the reasonable requirements of children, and where a party has a claim to compensation for a career given up for the family that the agreement ignores. Outside those, the court said, the parties' autonomy should ordinarily prevail. The cases since have applied that framework rather than expanding it.
HD v WB in 2023 is the modern example of the first category. The agreement had been freely entered into, but by the divorce the wife's fortune had grown and the agreement's provision for the husband did not address his needs; the judge departed from it to the extent of housing and an income and no further. Cummings v Fawn, the same year, set the measure: needs are a range from spartan to comfortable, and an agreement that leaves a party below the spartan end is corrected only just past it. Brack v Brack in the Court of Appeal added that a court departing from an unfair agreement may weigh all the section 25 factors, not needs alone, though a needs-based outcome is the norm. And on the other side of the line, Versteegh v Versteegh upheld an agreement signed without advice or disclosure because the wife understood it; absence of formalities is not, by itself, unfairness. Section 25 of the Matrimonial Causes Act 1973 supplies the yardstick throughout, with first consideration to any child under eighteen.
When is a prenup unfair? FAQs
What makes a prenup unfair?
Leaving a partner in need, or missing disclosure, advice or fair terms (see how to make a prenup fair).
When is fairness assessed?
At the time of the divorce, not the wedding day – which is why agreements need to be built to last.
Does a prenup have to be a 50/50 split to be fair?
No – unequal terms can be perfectly fair as long as both partners’ needs are met (see the needs principle).
Can an unfair prenup be partly upheld?
Yes – a court may follow most of it and top up provision to meet needs, rather than tear it up (see can a prenup be overturned?).
Who decides whether a prenup is fair?
The court, applying the Radmacher principle – the partner resisting the agreement must show why it would be unfair to enforce it.
How do I stop my prenup becoming unfair over time?
Provide fairly at the outset and include a review clause so you revisit it on big life events.
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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.