By Tracy Collins & Morgan Collens


Estate planning can be a minefield of confusing terminology, with the difference between mirror and mutual wills often misunderstood.

Mirror Wills, typically created by couples, mirror each other’s content, and can be altered or revoked by either will-maker at any time. Despite their reciprocal nature, they are distinct from Mutual Wills, which are legally binding and therefore harder to revoke. Mutual Wills involve an additional agreement between two individuals to create Wills on binding terms upon the surviving party, with equity imposing a trust.

Establishing the existence of Mutual Wills requires proving key elements. Clear evidence of an agreement among the parties is essential, along with specific terms indicating mutuality and irrevocability. The intention to create a legally binding contract through the executed Wills is crucial.

While oral agreements may be acceptable, the Courts emphasise the difficulty of proving the same, especially without the provision of a written contract.

While the final decision was handed down in 1937, the case of Birmingham v Renfrew remains particularly relevant when summarising the key aspects of Mutual Will agreements, including:

  1. Two parties can create a contract through making mutual Wills;
  2. While both parties are alive, the contract can only be altered or revoked with notice to the other;
  3. If the contract is broken without sufficient notice, either whilst both parties are alive or by the surviving party after the death of the first, this amounts to fraud;
  4. On the death of the first party, the contract becomes binding and irrevocable;
  5. The survivor is free to deal with the inherited assets on trust for the benefit of those named in the Will;
  6. Those named in the Will become beneficiaries of a constructive trust pursuant to the terms of the Will, with the survivor acting as trustee for their benefit and the trust capital is what is left after the survivor has enjoyed it; and
  7. Any transactions to defeat the intentions of the deceased party by the survivor will be in breach of that trust.

To avoid disputes relating to Mutual Wills, certain precautions are recommended:

  1. Seek legal advice to ensure correct drafting and suitability to specific requirements.
  2. Document the Mutual Will agreement thoroughly and execute them simultaneously, clearly reflecting the intent to create a binding contract.
  3. Regularly review and discuss the terms to align with the parties’ wishes, formalising alterations with the agreement of all involved parties.
  4. Consider the alternatives, like Testamentary Trusts, or other estate planning strategies which may be easier to amend in future.

Of course, despite both parties having the best intentions, disputes may still arise. If a party attempts to change a Will against a Mutual Will agreement, beneficiaries can seek court intervention to enforce the Mutual Will and protect their interests.

If you are interested in creating a Mutual Will, or you are concerned about the implications of the same, we strongly encourage contacting us at

*If you and your partner create mirror wills with the same lawyer, and then wish to alter it independently with this same lawyer again, they will likely request the consent of your partner before making any changes.


Disclaimer: This publication contains comments of a general and introductory nature only and is provided as an information service. It is not intended to be relied upon as, nor is it a substitute for specific professional legal advice. You should always speak to us and obtain legal advice before taking any action relating to matters raised in this publication.