Joint Wills vs Mirror Wills: What's the Legal Difference?

At a glance

• Mirror wills: two separate wills, one per partner, with matching or near-identical terms. Each is a standalone legal document.
• Joint wills: a single document intended as the will of two people. Legally possible but very rare in England and Wales, and generally discouraged.
• Mutual wills: mirror wills made together with a proven, legally binding agreement not to revoke — a distinct doctrine from case law (starting with Dufour v Pereira), not a form of document.
• Can the survivor change things? With ordinary mirror wills, yes — the survivor can make a new will at any time after the first death. With proven mutual wills, no — equity imposes a constructive trust on the survivor's estate.
• Statutory formalities: every will, whatever the arrangement, must meet section 9 of the Wills Act 1837 — in writing, signed, and witnessed by two witnesses present at the same time.
• Marriage revokes wills: under section 18 of the Wills Act 1837, marrying or entering a civil partnership after signing a will normally revokes it, unless the will expressly anticipates that specific marriage.
• No will at all: if either partner dies without a valid will, the Administration of Estates Act 1925 intestacy rules — not the couple's intentions — decide who inherits.

Mirror wills: two documents, matching terms

A mirror will is not a special legal category — it is simply the common description for what happens when two people, usually partners, each make their own separate will and choose to make the terms match. Typically each partner leaves everything to the other first, and then to the same beneficiaries (often their children) if the other has already died.

Because each mirror will is a standalone document, it must independently satisfy the formal requirements in section 9 of the Wills Act 1837: it must be in writing, signed by the testator (or by someone else in their presence and at their direction), and the signature must be made or acknowledged in the presence of two witnesses present at the same time, each of whom then signs or acknowledges their own signature in the testator's presence.

The key legal feature of an ordinary mirror will is that it creates no binding obligation on the survivor. After one partner dies, the survivor remains free to make an entirely new will and change who inherits — including replacing beneficiaries that the original mirror wills named. Couples sometimes assume that making matching wills "locks in" their joint wishes. It does not, unless something more is put in place (see mutual wills, below).

Joint wills: one document, two testators — and why they are rare

A joint will is a single document expressed to be the will of two people. Unlike a mirror will, there are not two separate instruments — there is one, which both parties sign.

Joint wills are not prohibited in England and Wales, but they are unusual in modern practice for practical and legal reasons:

• Probate mechanics. When the first party dies, the joint document has to be admitted to probate as that person's will, while remaining unexecuted as a will for the survivor, who is still alive. The same single document then has to be dealt with again on the second death. This creates administrative complications that two separate mirror wills avoid entirely.
• Implied irrevocability. Courts have historically treated a genuine joint will — particularly one that disposes of the couple's combined property as a single scheme — as carrying with it an inference that the parties intended it to be irrevocable after the first death, in the same way as mutual wills. That inference is not automatic, but it is a real risk that most solicitors prefer their clients avoid by using separate mirror wills instead, with a mutual wills agreement layered on top if the couple genuinely wants an irrevocable arrangement.
• Amendment difficulties. Because both parties' wishes sit in one instrument, updating the document to reflect one partner's changed circumstances (a new grandchild, a falling-out with a beneficiary) is harder than updating an individual will.

For these reasons, when people say they want a "joint will," what they are very often looking for is either an ordinary pair of mirror wills, or mirror wills combined with a formal mutual wills agreement.

Mutual wills: the doctrine that can bind a survivor

Mutual wills are a distinct legal doctrine, not a type of document. Two people make separate wills (which may look just like ordinary mirror wills) but do so under a contract or clear agreement that neither will revoke or change their will after the other's death without notice to the other.

The doctrine originates in the 18th-century case Dufour v Pereira, and has been considered in modern authority including Re Cleaver and the Court of Appeal decision in Re Goodchild. The principle: once the first party dies having relied on the agreement, equity will not allow the survivor to go back on it. The survivor can still, technically, make a new will — but the court will impose a constructive trust requiring their estate to be distributed in line with the original agreed terms regardless of what the later will says.

This is a significant legal consequence, so the courts require the agreement to be proved clearly. Case law describes the evidence needed as "certain and unequivocal" or "clear and satisfactory" — simply having two mirror wills with matching content is not, by itself, enough to establish a mutual wills agreement. There needs to be evidence of an actual agreement between the parties not to revoke, for example recorded in the wills themselves, in a separate written agreement, or in clear witness evidence of what was discussed and agreed at the time.

Because proving (or disproving) a mutual wills claim often turns on evidence created years earlier, couples who want this level of commitment are generally better served by recording the agreement clearly in writing at the time, rather than relying on a court inferring it later from matching wording alone.

What marriage and civil partnership do to any of these wills

Whichever structure a couple uses — mirror wills, a joint will, or mutual wills — a later marriage or civil partnership can undo it. Under section 18 of the Wills Act 1837, a will is automatically revoked by the testator's marriage, unless the will was made in clear contemplation of that specific marriage and states that it is not intended to be revoked by it. Section 18B applies the equivalent rule to entering a civil partnership.

This catches couples who make wills before their wedding or civil partnership ceremony without including the specific wording needed to protect the will. It is a particular risk for engaged couples who make mirror wills, or even set up a mutual wills agreement, ahead of a wedding date, assuming the arrangement will simply carry on afterwards. Unless the wording anticipates the marriage, it does not.

By contrast, section 20 of the Wills Act 1837 confirms that a will (once it survives marriage, or where no marriage is involved) can only be revoked by a later will or codicil, a written revocation executed like a will, or destruction with the intention of revoking it — it cannot simply lapse through the passage of time or a falling-out between partners.

If you die without any will at all

None of the arrangements above apply if a partner dies without ever having made a valid will. In that situation, the intestacy rules in the Administration of Estates Act 1925 (as amended) decide who inherits, based on a fixed order of family relationships rather than what the couple actually wanted.

Two points matter in particular for couples considering mirror wills:

• A surviving spouse or civil partner does not automatically inherit the whole estate if there are children — broadly, they receive personal possessions, a statutory legacy, and a share of what remains, with the rest passing to the children.
• An unmarried partner has no automatic entitlement at all under the intestacy rules, however long the relationship. If one partner in an unmarried couple dies without a will, the survivor can be left with nothing from the estate by law, regardless of what the couple intended.

This is one of the strongest practical reasons couples make matching wills in the first place — even simple mirror wills put the couple's actual wishes ahead of a default statutory order that may not reflect their family at all. See GOV.UK's guidance on who inherits if someone dies without a will.

Which approach fits your situation

• A first marriage, straightforward family, no blended-family complications: ordinary mirror wills are usually sufficient, and can each be changed individually if circumstances change.
• A blended family, or concern that a survivor might later redirect the estate away from children from the relationship: consider whether mutual wills, or a trust structured into the will (see our guide on types of wills in the UK), better protects the intended beneficiaries.
• A wedding or civil partnership ceremony planned after the wills are signed: make sure the wording expressly anticipates that marriage, or plan to make new wills shortly after the ceremony.
• An unmarried couple: wills of some kind are particularly important, given the absence of automatic intestacy rights for unmarried partners.

Getting it right

1. Decide what you actually want to achieve. If you simply want matching wishes recorded, ordinary mirror wills are usually enough. If you want to prevent the survivor from later changing the arrangement, you need to think about mutual wills or a trust, not just matching wording.
2. Make sure each will meets the formal requirements. Every will must independently satisfy section 9 of the Wills Act 1837 — writing, signature, and two witnesses present at the same time.
3. Record any agreement not to revoke clearly, in writing, at the time. If you want a mutual wills arrangement, do not rely on matching content alone to prove it later — the courts require clear evidence of the agreement itself.
4. Check the position if a wedding is coming up. If you are engaged or planning a civil partnership, make sure your wills either include wording anticipating that specific event, or plan to remake them soon afterwards.
5. Review after any major change. A new child, a new relationship, a change in assets, or a change in family circumstances is a reason to revisit any will, mirror or otherwise.

This guide provides general information about joint wills, mirror wills and mutual wills in England and Wales. It is not legal advice and is not a substitute for advice tailored to your specific circumstances. The law described here is subject to change — always check GOV.UK and legislation.gov.uk for the most current position.

Last reviewed: July 2026 by a non-practising solicitor · Next review due: July 2027 or on legislative change.