What Makes a Will Invalid?

Most invalid wills fail for avoidable reasons

Will invalidity sounds dramatic but most cases are not contested in court — they are simply wills that fail quietly because a formality was not observed. The estate then falls into intestacy, or a previous will comes back into effect.

Here are the main ways a will can be invalid.

Improper execution

A will must be signed by the testator in the presence of two witnesses who are both present at the same time. The witnesses must then sign in the testator's presence. All three signatures must be on the same document.

Common mistakes: the testator signs before the witnesses arrive; one witness signs in a different room; the will is signed in sections over multiple sittings; witnesses sign in the wrong order. Any of these can invalidate the will.

A beneficiary witnessing the will does not invalidate it, but it does invalidate that beneficiary's gift. The same applies to the spouse or civil partner of a beneficiary.

Lack of testamentary capacity

The person making the will must understand what they are signing, know broadly what they own, and not be suffering from any condition that prevents them from making a free decision. This is the test from Banks v Goodfellow (1870).

Dementia, stroke, or serious illness does not automatically mean a person lacks capacity. Capacity is assessed at the time of signing, not generally. But if a will is challenged on capacity grounds, the burden of proof matters — and a will made without any supporting evidence of capacity is harder to defend.

Undue influence

A will can be set aside if it was made because someone pressured or coerced the testator. Undue influence is hard to prove — it requires showing that the testator's free will was overborne, not merely that they were persuaded or that someone had influence over them.

Courts are cautious about undue influence claims. A strong relationship, even a controlling one, is not enough. But where there is evidence of isolation, dependency, or direct pressure at the time of signing, a claim may succeed.

Fraud and forgery

A will produced by fraud — for example, where the testator was deceived about what they were signing — or by forgery is void.

Revocation

A will is revoked in three ways: by the testator writing a new will that includes a revocation clause; by the testator deliberately destroying the original; or by marriage. Getting married in England and Wales automatically revokes any existing will. This is one of the most commonly overlooked traps.

Divorce does not revoke a will, but it does change its effect — the former spouse is treated as having died before the testator.

Ambiguity and drafting errors

A will that is ambiguous — where the meaning is genuinely unclear — is not invalid but can cause serious problems. Courts will try to determine what the testator intended, but this takes time and money. Clear, precise drafting avoids it.

How to protect your will

Sign correctly, in front of two independent witnesses who are not beneficiaries. If there is any question about your capacity, have your GP assess you first. Keep your will updated when circumstances change. Store the original safely and tell your executor where it is.