Can Someone Have Capacity One Day and Not the Next?

15th June 2026

You might be wondering whether Can Someone Have Capacity One Day and Not the Next? is a real possibility. The short answer is yes. Mental capacity isn’t a fixed state. Some people may be perfectly able to make a decision one moment, but struggle to make that same decision later due to things like illness, medication, fatigue or a fluctuating medical condition.

Understanding Fluctuating Capacity

Many people assume capacity is something you either have or don’t have.

In reality, it’s often more nuanced than that.

The law recognises a person’s ability to make decisions can change over time. Capacity is both decision-specific and time-specific.

For example, someone living with early-stage dementia may be able to make decisions about their finances on a good day, but struggle when they’re tired, unwell or confused another time.

Similarly, a person recovering from a stroke may have periods where they can clearly understand information and communicate their wishes, followed by periods where they can’t.

The key point is that capacity is assessed at the time the decision is being made.

Common Causes of Changing Capacity

Fluctuating capacity can occur for several reasons.

Dementia is probably the most common example. Some individuals experience significant variations in their cognition on any given day to day.

Delirium, caused by infections, dehydration or medication side effects, may also temporarily affect someone’s ability to make decisions.

Mental health conditions can sometimes have a similar effect, particularly when symptoms are at their most severe.

Even something as simple as extreme tiredness, pain or hospital treatment can temporarily reduce a person’s ability to understand and process information.

That’s why professionals are encouraged to assess mental capacity carefully, rather than making assumptions based on a diagnosis alone.

Why Timing Matters for an LPA

When creating a LPA, the person making it absolutely must have the mental capacity to understand what they’re signing.

If capacity fluctuates, it may still be possible to put an LPA in place during a period when the individual is able to understand the document and its implications.

Waiting for the right moment can be a risky proposition though.

A condition that currently causes occasional confusion may progress to the point where your capacity is lost, full stop.

At that stage, it’s usually too late to create an LPA.

Families are then often forced to consider a Court of Protection deputyship application instead, which can be more expensive and time-consuming in the long run.

Planning While Choices Are Still Available

Many families first notice fluctuating capacity through small changes in behaviour.

A parent forgets important conversations. A partner becomes confused about financial matters they previously managed with ease. Good days and bad days begin to merge. Situations can be difficult to interpret, particularly because the person may appear completely capable for much of the time.

That uncertainty is often a signal to start planning rather than waiting.

An LPA created using a service like Power of Attorney Online doesn’t take away someone’s independence. Instead, it creates a safety net so that trusted people can step in if a time comes when decisions can no longer be made independently.

For families facing changing capacity, having those arrangements in place early can provide reassurance, clarity and far more choice about what happens next down the line.