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Wills

What Makes a Will Invalid?

A will is usually invalid when it fails the signing and witnessing rules, or where the person lacked the capacity, knowledge or free will to make it.

8 min read · Written by the Fairchild Oldfield team · Last reviewed: July 2026

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The number of witnesses, both over 18, who must watch you sign your will and then sign it themselves for it to be valid in England and Wales.
Source: gov.uk, as at July 2026, subject to change.

A will is invalid in England and Wales when it does not meet the formal rules for making a will, or where the person who made it lacked the mental capacity, the knowledge of its contents, or the free will to do so.

The most common failures are practical ones around signing and witnessing. Others are harder to spot, such as a will made under pressure, or an earlier will that a later marriage has quietly cancelled. This guide sets out the main reasons a will can fail, drawing on the rules at gov.uk (as at July 2026, subject to change). It forms part of our wider estate planning guide, and sits alongside our note on How to Write a Will.

What makes a will invalid?

A will is generally invalid where it breaks the formalities in section 9 of the Wills Act 1837, or where the person lacked capacity, did not know and approve its contents, or was pressured into it. In England and Wales a valid will must be made in writing, by someone aged 18 or over who is of sound mind and acting voluntarily, and signed in the presence of two witnesses who are both over 18 (gov.uk, as at July 2026, subject to change).

The legal rules a valid will must meet

To be valid in England and Wales, a will must satisfy several conditions together, and failing any one of them can be enough to make it ineffective. The core requirements come from gov.uk guidance and section 9 of the Wills Act 1837 (legislation.gov.uk, as at July 2026, subject to change). The table below sets them out.

RequirementWhat it means
Aged 18 or overThe person making the will must generally be at least 18.
In writingThe will must be a written document, not merely spoken.
Of sound mindThe person must have the mental capacity to understand what they are doing.
Made voluntarilyIt must be their own free choice, not the product of pressure.
Signed correctlySigned in the presence of two witnesses who are both over 18.
Witnessed correctlyBoth witnesses sign in the presence of the person making the will.

Source: gov.uk, make sure your will is legal and Wills Act 1837, section 9, as at July 2026 and subject to change.

The most common failure

Signing and witnessing mistakes

Signing and witnessing errors are the usual reason a will fails, because the rules are strict. The person must sign in the presence of two witnesses who are both over 18, and each witness must then sign while the person making the will watches. Both witnesses must have a clear view of you signing, and you must have a clear view of each of them signing (gov.uk, as at July 2026, subject to change).

There is also a trap around who may witness. You cannot leave your witnesses, or their married partners, anything in the will, and a gift to a witness is generally void even though the will itself may still stand (gov.uk, as at July 2026, subject to change). For a fuller walkthrough, see our note on witnessing a will.

Two independent witnesses

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Two witnesses, both over 18, must see you sign and then sign themselves, and neither they nor their spouses should be beneficiaries (gov.uk, as at July 2026, subject to change).

Mental capacity, knowledge and approval

A will can be invalid where the person did not have the mental capacity to make it, or did not know and approve what it said. Gov.uk requires the person to be of sound mind and to make the will voluntarily (gov.uk, as at July 2026, subject to change). Where a serious illness or a condition such as dementia is present, capacity at the time of signing can later be questioned, which is one reason many people take care to record it.

  • Sound mind. The person must understand that they are making a will and broadly what it does.
  • Knowledge and approval. They must know and approve the contents, not sign something they have not understood.
  • Evidence. Where capacity might be doubted, a contemporaneous medical opinion is one option some consider.

Undue influence, fraud and forgery

A will made because someone was pressured, deceived or impersonated is not a valid expression of that person's wishes. Because a will must be made voluntarily (gov.uk, as at July 2026, subject to change), a will procured by undue influence, fraud or forgery can be challenged after death. These claims are often difficult to prove, and they overlap with the wider question of contesting a will, so they generally call for legal advice rather than self-help.

Undue influence is more than persuasion. Ordinary family discussion, or a relative expressing a hope about a gift, is not usually enough. The concern arises where free choice is overborne, for example coercion of a frail or dependent person. Because the line is fact-sensitive and the burden of proof sits with the person challenging the will, this is an area where many people choose to take advice from a qualified professional.

When a valid will stops working

Marriage, revocation and improper changes

I

Later marriage

Getting married generally cancels any earlier will, so it no longer applies. Source: gov.uk, as at July 2026, subject to change.

II

Deliberate revocation

Destroying a will by burning or tearing it up, intending to revoke it, can cancel it. Source: gov.uk, as at July 2026, subject to change.

III

Informal edits

You cannot amend a will once signed and witnessed; changes need a codicil. Source: gov.uk, as at July 2026, subject to change.

IV

A later valid will

A new, properly executed will usually replaces the one before it.

A worked example (illustration only). A man signs a will at home while only one neighbour is present, and a second neighbour signs the next day without the man there. Because the two witnesses did not both see him sign, and he did not see the second witness sign, the will fails the presence rule (gov.uk, as at July 2026, subject to change). If there is no earlier valid will, the estate would generally pass under the intestacy rules instead, under which an unmarried partner receives nothing (gov.uk, as at July 2026, subject to change). Every case turns on its own facts, so this is general information rather than a ruling on any real will.

What happens if a will is invalid?

If a will is invalid, the law looks to the most recent valid will instead, and if there is none, the estate passes under the intestacy rules. Those rules set a fixed order of who inherits, and they do not provide for unmarried partners or stepchildren (gov.uk, as at July 2026, subject to change). The outcome may be very different from what the person intended, which is why the formalities matter as much as the wishes.

A will that says the right thing but is signed the wrong way can still fail, and the intestacy rules then decide who inherits.

Where an invalid will has been discovered, or where family members disagree about validity, the position can be complex. Beneficiaries sometimes reach a different distribution by agreement, and there are formal routes for challenging or correcting a will after death. These paths carry deadlines and cost, so many people choose to take advice early rather than act alone.

Will validity in Scotland and Northern Ireland

This guide describes the law of England and Wales, where the section 9 formalities apply (legislation.gov.uk, as at July 2026, subject to change). Scotland has its own succession law, with different execution rules and legal rights that can entitle a spouse and children to a fixed share whatever the will says. Northern Ireland has a separate but broadly similar system to England and Wales. Where an estate touches more than one UK nation, it can be worth taking advice in each.

Frequently asked questions

Does a will need to be signed and witnessed to be valid?

Yes, in England and Wales. The will must be signed by the person making it in the presence of two witnesses who are both over 18, and each witness must then sign while that person watches (gov.uk, as at July 2026, subject to change). A will that misses these steps is generally invalid, whatever it says about who should inherit.

Can a beneficiary witness a will?

They can physically witness it, but it usually backfires. You cannot leave your witnesses, or their married partners, anything in the will, and a gift to a witness is generally treated as void even though the rest of the will may stand (gov.uk, as at July 2026, subject to change). Many people choose two independent witnesses to avoid losing a gift by accident.

Does getting married make a will invalid?

Generally yes in England and Wales. Getting married cancels any will made beforehand, so an earlier will no longer applies unless it was made in contemplation of that marriage (gov.uk, as at July 2026, subject to change). Reviewing a will after marriage, divorce or a new child is something many people do to keep it current.

Can you change a will after it has been signed?

Not by writing on it. You cannot amend a will once it has been signed and witnessed; the way to change it is a codicil, which needs the same signing and witnessing as the will itself, or a new will (gov.uk, as at July 2026, subject to change). Obvious later alterations on the face of a will are generally disregarded.

What happens to the estate if a will is invalid?

The estate falls back on the last valid will, and if there is none, on the intestacy rules. Those rules set a fixed order of inheritance and make no provision for unmarried partners or stepchildren (gov.uk, as at July 2026, subject to change). The result can differ sharply from what the person wanted, so validity is worth getting right first time.

Can an invalid will be challenged or corrected after death?

Sometimes. Where validity is in doubt, a will can be contested, and there are separate routes for correcting clear drafting errors, each with deadlines and cost. Because these claims are fact-sensitive and time-limited, it can be worth discussing the position with a qualified professional early, rather than waiting. See our guide to contesting a will.

About Fairchild Oldfield

The Fairchild Oldfield team brings together estate planning, tax, independent financial advice and client care, working with families across England and Wales.

Fairchild Oldfield are estate planning specialists and will writers, not a firm of solicitors. This article is general information based on practical experience, not legal, tax or financial advice.

Important: This article is general information only and is not legal, tax or financial advice. Reading it does not create a professional relationship. It is based on the law of England and Wales, and other UK jurisdictions may differ. Figures and rules are current as at July 2026 and are subject to change. Before acting, many people choose to seek advice from a suitably qualified professional, such as a solicitor, a STEP practitioner, an accountant, or an FCA-authorised financial adviser, who can consider your individual circumstances.

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