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Testamentary Capacity Challenges in Ontario Estates

Worried a loved one did not understand their will because of dementia? Learn the Ontario capacity test, who must prove it and how courts weigh the evidence.

Wills & Estates5 min readTSLBy the Treadstone Law Team · OntarioUpdated October 28, 2026
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Key takeaways
  • Ontario courts ask whether the person understood what a will does, what property they had, and who had claims on them.
  • The person defending the will carries the legal burden of proving capacity, and that burden can return to them when suspicious circumstances raise doubt.
  • Estate disputes follow the ordinary costs rules, and courts can order the loser to pay part of the other side's costs.

When someone with memory loss or dementia dies and leaves a will that surprises the family, the first question is often whether they really understood what they were signing. That question is about testamentary capacity, and it is one of the most common reasons families end up in estate court.

This article explains the test Ontario courts use, who has to prove what, and how a capacity dispute usually unfolds. It is general information only. Capacity cases turn heavily on their facts, so a lawyer should look at your situation before you decide how to proceed.

What testamentary capacity means

Testamentary capacity is the mental ability needed to make a valid will. Ontario applies a long-standing test from English case law. Under it, the person making the will must understand the nature and effect of a will, understand the property they are disposing of, and understand the claims that ought to be given effect to.

The test also asks whether a disorder of the mind poisoned their affections or whether an insane delusion influenced how they divided their property. In plain terms, the court is asking whether the person could grasp what they were doing and who might reasonably expect to be remembered.

Capacity is not the same as wisdom or fairness. A person may leave a surprising will and still meet the test. The legal question is about understanding, not about whether the family agrees with the result.

Who has to prove what

The person asking the court to accept the will is called the propounder, and is usually the estate trustee named in it. That person carries the legal burden of proving due execution, knowledge and approval of the contents, and testamentary capacity.

A challenger cannot simply allege incapacity and sit back. They can meet their initial evidential burden by pointing to suspicious circumstances that, if accepted, would tend to show the person did not know and approve the contents or lacked capacity. Once that is done, the legal burden reverts to the propounder. Where suspicious circumstances raise a real doubt about capacity, the propounder must prove capacity on a balance of probabilities.

QuestionWho carries the burden
Was the will properly signed and witnessed?The person propounding the will
Did the person know and approve the contents?The person propounding the will
Did the person have capacity?The person propounding the will, and again if suspicious circumstances raise doubt
Was there undue influence?The person attacking the will

What evidence tends to matter

Courts look at the whole picture around the time the will was made. Typical sources include the following.

Proof of signing also matters. In a contested case, a court looks for two witnesses present at the same time who saw the person sign. In one Court of Appeal decision, the judge found insufficient proof of the formalities where only one interested person gave uncorroborated evidence, and also noted probable lack of capacity and suspicious circumstances.

Starting and running a challenge

If you object to an estate trustee getting probate, you can file a notice of objection. Court staff then notify the applicant, who must send you a notice to objector and file it with the court along with an affidavit of service. A notice of objection other than to accounts has a court filing fee of $94.00. In one Court of Appeal case, because of an objection the registrar could not issue probate and a probate order from a judge was required, which shows an objection can add delay and complication.

Mandatory mediation applies to specified estate proceedings, including claims against an estate, and mediation directions normally form part of a motion for directions. If a child's interest is affected, such as in a will challenge, the Office of the Children's Lawyer must be served.

There is also a point about time. A proceeding seeking only a declaration, for example that a will is valid or invalid, with no other relief sought, has no limitation period. If you also seek other relief, the ordinary two-year period may matter, so get advice early rather than assuming you have time.

Costs and risk

Estate litigation is governed by the ordinary civil costs regime. Costs come out of the estate only where public policy considerations apply, such as giving effect to valid wills of competent testators, ensuring estates are properly administered, or litigation caused by the testator. Courts can make blended orders where the loser pays part of the other side's costs and the estate bears the rest.

In one example, a daughter's application to stop distribution of her mother's estate failed at the threshold, and she was ordered to pay $8,758.19 in costs of the application and $15,000 in partial indemnity costs of the appeal. That is a case-specific outcome, not a prediction, but it shows that an unsupported challenge can be expensive.

What to do next

Frequently asked questions

Does a dementia diagnosis mean the will is invalid?

Not automatically. The court asks whether the person understood the nature and effect of a will, their property and the claims on them when the will was made. A diagnosis is relevant evidence, but it is not the whole answer.

Who has to prove the person had capacity?

The person asking the court to accept the will carries the legal burden of proving capacity, along with due execution and knowledge and approval of the contents. Where suspicious circumstances raise doubt, that person must prove capacity on a balance of probabilities.

Is there a deadline to challenge a will?

A proceeding seeking only a declaration about validity has no limitation period. The basic limitation period for other claims is two years from discovery. Which rule applies depends on what you ask the court for, so confirm with a lawyer.

Who pays for a capacity dispute?

The ordinary civil costs rules apply, and costs come from the estate only in limited public policy situations. Courts can also split costs between the losing party and the estate.

Sources

Links go to official government, court and regulator pages. The law changes — confirm you are reading the current version.

This article is general information, not legal advice. Reading it does not create a lawyer-client relationship. Ontario laws, tax rates, and government programs change, and how the law applies depends on your specific facts. For advice about your situation, speak with a licensed Ontario lawyer. Treadstone Law is licensed by the Law Society of Ontario — reach us at 1-844-900-1070 or start a file online.

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