What is mental capacity?
Mental capacity is the ability to make a particular decision at the time it needs to be made. It is not a label for a person. Someone can have the capacity to decide what to eat and not the capacity to sell their house, on the very same afternoon.
In England and Wales the test comes from the Mental Capacity Act 2005. It has two stages, and both have to be met before the law treats someone as lacking capacity.
What is the legal test?
The first stage is in section 2 of the Mental Capacity Act 2005:
“For the purposes of this Act, a person lacks capacity in relation to a matter if at the material time he is unable to make a decision for himself in relation to the matter because of an impairment of, or a disturbance in the functioning of, the mind or brain.”
So there has to be something wrong with the working of the mind or brain, and it has to be the reason the person cannot decide. Dementia, a stroke, a brain injury and the effects of medication can all count. It does not matter whether the problem is permanent or temporary.
The second stage is in section 3 of the Mental Capacity Act 2005. A person is unable to make a decision if they cannot do any one of four things:
- Understand. Take in the information relevant to the decision.
- Retain. Hold on to that information. Holding it only for a short while is still enough.
- Use or weigh. Use the information as part of making the decision.
- Communicate. Get the decision across, by talking, by signing, or by any other means.
Failing on any one of the four is enough. The information a person has to understand includes what is reasonably likely to happen if they decide one way, the other way, or not at all.
Capacity is about one decision at one moment
Two phrases in section 2 do a lot of work. Capacity is judged in relation to a matter, and at the material time.
That is why nobody “has capacity” or “lacks capacity” in general terms. The question is always about one decision, on one day. A person with fluctuating capacity may be able to make a will in the morning and not in the evening. This is also why evidence recorded at the time is worth so much more than an opinion formed years later.
The five principles
Section 1 of the Mental Capacity Act 2005 sets out five principles that govern everything else:
- Assume capacity. A person must be assumed to have capacity unless it is established that they lack it.
- Help first. Nobody is to be treated as unable to decide until all practicable steps to help them have been tried without success.
- An unwise decision is still a decision. A person is not to be treated as unable to decide merely because the decision is unwise.
- Best interests. Anything done for someone who lacks capacity must be in their best interests.
- Least restrictive. Before acting, consider whether the aim can be achieved in a way that interferes less with the person’s rights and freedom.
The third principle is the one families most often get wrong. Choosing to leave your estate to a neighbour rather than your children may surprise everyone. On its own it proves nothing about capacity. A lack of capacity also cannot be established merely from someone’s age, their appearance, or behaviour that leads others to make unjustified assumptions.
Where the question reaches a court, it is decided on the balance of probabilities.
Does this test apply to wills?
No, and this catches people out. The Act sets out its test for the purposes of this Act
. The capacity to make a will has its own, older test, from Banks v Goodfellow in 1870.
Banks v Goodfellow is still the test for a will. The Court of Appeal applied it in Hughes v Pritchard [2022] EWCA Civ 386. It recorded at [62] that both the trial and the appeal proceeded on the basis that the test remains that set out in Banks v Goodfellow
. In Clitheroe v Bond [2021] EWHC 1102 (Ch) Falk J agreed with two earlier High Court decisions that it has not been swept away by the MCA
.
This may change one day. In May 2025 the Law Commission recommended that the Mental Capacity Act test should replace Banks v Goodfellow for wills, and published a draft Wills Bill alongside its report. That is a recommendation and not law. No Bill has been put before Parliament, so the older test still governs.
Our guide to testamentary capacity covers the will test itself. Our article on Hughes v Pritchard covers what that case decided.
What this means in practice
If you are making a will or a lasting power of attorney, capacity is the ground everything else stands on. It is also the thing that gets challenged after you have died, when you cannot answer for yourself. Recording evidence of your capacity at the moment you make the document is the one thing that cannot be done later.
This article is for general information and is not legal advice. Capacity Vault records evidence of capacity. It is not a doctor’s assessment. If you are worried about capacity in your own situation, please get in touch.
Sources
- Mental Capacity Act 2005, section 1 on legislation.gov.uk
- Mental Capacity Act 2005, section 2 on legislation.gov.uk
- Mental Capacity Act 2005, section 3 on legislation.gov.uk
- Hughes v Pritchard [2022] EWCA Civ 386 on Find Case Law
- Hughes v Pritchard [2022] EWCA Civ 386 on BAILII
- Clitheroe v Bond [2021] EWHC 1102 (Ch) on Find Case Law
- Clitheroe v Bond [2021] EWHC 1102 (Ch) on BAILII
- Mental Capacity Act 2005 Code of Practice on GOV.UK
- Modernising Wills Law, final report and draft Bill, on the Law Commission website
