Assessing capacity

Assessing a patient's capacity is essential for doctors and it’s important to take all practicable steps to help patients make decisions. Here's what you need to know.

Assessing a patient's capacity

  • Assessing capacity is part and parcel of being a doctor.
  • A patient's ability to make a decision about treatment is central to the doctor-patient relationship.
  • It's important take all practicable steps to help a patient make the decision themselves.
  • Capacity is time and decision specific.

What is capacity?

Capacity is the ability to make a decision or take an action that impacts on a person's life. It indicates that a person is able to make a decision about their own care and treatment.

If you're caring for someone who might lack capacity to consent, or decline a treatment or proposed course of action, you need to assess their capacity first.

The Mental Capacity Act

Assessment of capacity is set out in the Mental Capacity Act (MCA) 2005 and its accompanying Code of Practice.

It provides a framework for caring for or treating people 16-years old or over in England and Wales who lack the ability to make decisions for themselves.

  • The MCA requires you to assess a patient's capacity before treatment.
  • Capacity is time and decision specific. This means you should assess a patient's ability to make a specific decision at the time the decision needs to be made.
  • You shouldn't decide that someone lacks capacity based solely on their age, appearance, condition or behaviour.
  • A person's inability to make a major or complex decision doesn't mean they can't make a smaller or simpler decision.

The MCA embodies five key principles. The first three help you determine whether a patient lacks capacity. If they do, the final two principles are used to support the decision-making process.

Principle 1: the presumption of capacity

  • Capacity should be assumed unless proved otherwise.
  • Don't assume someone is unable to make a decision based on their medical condition or disability.

Principle 2: support the individual

  • A patient should be given all practicable help before they are deemed unable to make their own decisions.
  • Make every effort to support a patient in making a specific decision for themselves if possible (eg, providing support through an advocate, translator, speech and language therapist etc.).
  • Even if you establish the patient lacks capacity, you should still involve them as far as possible in making their decision.

Principle 3: unwise decision

  • A patient has the right to make a decision that you might disagree with or consider irrational or unwise.
  • This doesn't indicate a lack of capacity, but may reflect individual preferences or values.
  • The ability to make the decision is key; not the decision itself.

Principle 4: best interests

  • Decisions made or action taken for or on behalf of a person who lacks mental capacity must be done in their best interests.
  • 'Best interests' isn't defined by the MCA or the Code of Practice, and depends on individual circumstances. These include a person's welfare, social, emotional and psychological interests as well as their medical interests.
  • Consider the patient's current or previous wishes and their beliefs and values (although these are not, in and of themselves, decisive).

Principle 5: least restrictive option

  • If you're making a decision on behalf of a person lacking capacity, you must consider whether it's possible to delay until the person regains capacity.
  • If a decision is needed, consider if you can do so while interfering with the person's rights or freedoms as little as possible.
  • If a person is temporarily incapacitated and you can defer the decision until they regain capacity, do so.
  • If this isn't possible, make the decision in the person's best interests. The least restrictive option must be considered wherever possible.

Decision making

Determining whether someone has the capacity to make a particular decision involves a two-stage test.

  • Stage 1: whether there is an impairment of or disturbance in the functioning of the patient's mind or brain, whether temporary or permanent.

If so, then:

  • Stage 2: is the impairment or disturbance sufficient that the person is unable to make a particular decision at the time it needs to be made?


The MCA states that someone is unable to make a decision if they cannot do one or more of the following:

  • understand the information relevant to the decision (including the reasonably foreseeable consequences of whatever decision is made or of failing to make a decision)
  • retain that information in making the decision
  • use or weigh the information available, and
  • communicate the decision by any means, including speech, sign language, or simple muscle movement.

A person failing one or more aspects of this test is deemed to lack the relevant capacity, but you must try to find ways of communicating with a patient before determining they lack capacity.

You might need to consider the views of those close to the patient (family, friends, carers or other professionals), but whether a patient lacks capacity is your decision to make.


  • Record why there is uncertainty about the patient's capacity, as well as details of your assessment and conclusions.
  • The record should clearly show how any decision about the patient's best interests was reached, the reasons for the decision, who was consulted, and what factors were considered.

You should only make a decision for or on behalf of a patient after it's been determined they lack the capacity to do so themselves. Any decision should be made in their best interests.

The MCA provides further guidance on the factors that a decision-maker acting on behalf of a patient should consider in deciding what is in a person's best interests.

This page was correct at publication on 27/06/2019. Any guidance is intended as general guidance for members only. If you are a member and need specific advice relating to your own circumstances, please contact one of our advisers.