What is a mutual will? What every couple should understand before signing

You’ve both worked hard to build a life together. You want to make sure the people you love are protected when you’re gone. That’s a completely reasonable thing to want. But if you’re considering mutual wills as part of your estate planning, it’s worth understanding exactly what you’re agreeing to before you sign anything.

Lotus Legal helps families across Western Australia think through these decisions carefully, without the legal jargon and without the nasty surprises.

What is a mutual will?

A mutual will is more than just two people writing similar wills. It’s a legally binding contract between two people (usually spouses or de facto partners) to make their wills in agreed terms and not change those terms after one of them has passed away.

That distinction matters. The agreement itself is what creates the legal obligation. Without it, you simply have two separate wills that happen to look alike.

Mutual wills are often used in blended family estate planning, where a couple wants to provide for the surviving spouse while also protecting children from a previous relationship. For example, a husband and wife might agree that after the first death, the survivor will leave the estate to both sets of children equally, rather than having full freedom to change that arrangement later.

For a mutual will agreement to be enforceable, there must be clear evidence that both people genuinely intended to create a binding arrangement. A handshake or a conversation is rarely enough.

How mutual wills work

A well-drafted mutual wills agreement should cover:

• Which assets are included
• Who the agreed beneficiaries are
• What the surviving spouse or partner can and cannot do with those assets
• What happens if one party loses capacity
• What happens if the survivor remarries or enters a new relationship
• Whether the agreement can be changed while both parties are still alive

While both parties are alive and have capacity, the arrangement can usually be varied by mutual consent.

Once one party dies after relying on the agreement, the survivor may be bound by its terms. If the survivor then makes a new will or transfers assets in a way that defeats the agreed beneficiaries, those beneficiaries may have legal grounds to challenge that.

Courts in WA have dealt with exactly this kind of dispute. In Fazio v Fazio [2024] WASC 114, the court considered a claim based on an alleged mutual wills agreement and highlighted just how important clear, written evidence of the parties’ intentions really is. Relying on an oral agreement is a significant risk.

Mirror wills, mutual wills and joint wills: what’s the difference?

This is one of the most common points of confusion, and it’s worth getting right.

Type	What it means
Mirror wills	Two separate wills with similar or identical terms. No binding agreement. Either party can change their will at any time.
Mutual wills	Two separate wills plus a binding agreement not to change the agreed terms after the first death.
Joint wills	A single document signed by both people. Rare in WA and generally not recommended.

Mirror wills are common and straightforward. They don’t create any legal obligation between the two parties. Mutual wills go a step further by adding a contract. That’s what makes them more complex and more powerful in the right circumstances.

What mutual wills can and can’t do

They can help you:

• Provide greater certainty about how estate assets will eventually be distributed
• Protect your own children from a prior relationship
• Balance the interests of a surviving spouse with other beneficiaries
• Reduce the risk of the survivor changing the estate plan after you’re gone

They generally cannot:

• Override the Family Provision Act 1972 (WA), which allows eligible dependants to make a family provision claim regardless of what the wills say
• Stop the surviving spouse from spending assets on their own reasonable living expenses or retirement needs
• Physically prevent the survivor from making a new will (though a new will that breaches the agreement may give rise to legal remedies)
• Guarantee that estate assets remain unchanged until the second death

That last point is important. The survivor isn’t frozen in place. They can still live their life, spend money, and meet their own needs. What they may not be able to do is give assets away or transfer them in a way that’s designed to defeat the agreed beneficiaries.

The risks worth knowing about

Mutual wills can offer real certainty, but they can also create problems if they’re not done carefully.

The biggest risk is inflexibility. Life changes. Financial circumstances shift. A surviving spouse who is bound by an agreement made years earlier may find themselves in a difficult position if their needs have changed significantly.

Other risks include unclear wording, disputes about which assets are covered, difficulty proving an oral agreement existed, and conflict between blended family members. According to the Australian Institute of Family Studies, around 12% of Australian couple families are step- or blended families, and those family dynamics can make estate disputes more likely, not less.

Before entering a mutual wills agreement, it’s worth considering whether other estate planning strategies might achieve a similar result with more flexibility. Testamentary trusts, life interests, binding death benefit nominations, and changes to property ownership structures are all worth exploring.

Talk to our friendly team about your estate planning

Estate planning decisions like this deserve careful thought and advice that’s tailored to your circumstances. Whether you’re part of a blended family, looking to protect children from a previous relationship, or simply want to understand your options, we’re here to help.

Our Perth lawyers offer fixed-fee estate planning advice with no hidden costs. We work with clients across Balcatta, Rockingham, Jurien Bay, Northam, and the wider Perth metro area. You can also explore our full range of legal services or learn more about deceased estate matters if you’re dealing with a loved one’s estate.

Get in touch with our team today for a conversation about your situation.