Having mental capacity means being able to make your own decisions and understand the consequences of those decisions. No one can make a decision on your behalf unless it can be shown that you lack mental capacity.
If you lack mental capacity for a decision, it means you're unable to do one or more of the following:
understand the information relating to the decision
weigh up that information
remember that information for long enough to make your decision
communicate your decision (whether verbally, using sign language, or by other means).
However, whether someone has mental capacity can change depending on the decision – so someone might be able to make decisions about certain things but not others. Others might be able to make a decision at a certain time, but unable to make the same decision at another time. This is why anyone considering whether you have mental capacity needs to consider your ability to make and communicate a specific decision at the time it needs to be made.
You should be given as much help as possible to make and communicate a decision before anyone judges that you lack mental capacity.
Taking time to weigh up or communicate a decision shouldn't be mistaken for a lack of mental capacity. Nor should having a certain condition, such as dementia. For example, someone may still have capacity to make certain decisions for some time following a diagnosis.
Find out more about mental capacity on GOV.UK