Capacity & Consent in Adults

🧭 When to assess capacity

Mental capacity is the ability to make a specific decision at the time it needs to be made. The Mental Capacity Act 2005 (MCA) governs this in England and Wales, and you always begin from the presumption of capacity – an adult is assumed to have capacity unless it is established, on the balance of probabilities, that they do not.

Assess capacity only when there is a reasonable doubt about a person's ability to make the decision in front of you, and where that doubt arises from an impairment of, or disturbance in the functioning of, the mind or brain – for example dementia, delirium, learning disability, acquired brain injury, severe mental illness, acute confusion, or intoxication. The assessment is decision-specific (capacity to consent to a flu jab is not the same as capacity for major surgery) and time-specific (capacity can fluctuate, so it may be present in the morning but not the evening).

For routine, low-stakes care you act on a reasonable belief about capacity; a formal, documented assessment is reserved for significant, serious or contested decisions. An assessment is not triggered simply because a person makes an unwise decision, carries a diagnosis, or is judged by their age or appearance – none of these displaces the presumption of capacity.

Source: Mental Capacity Act 2005 · NICE NG108