The legal test

The Equality Act 2010 defines disability in words that look straightforward and conceal considerable complexity.

What the statute says

Section 6 of the Equality Act 2010 sets out the core definition: a person has a disability if they have a physical or mental impairment that has a substantial and long-term adverse effect on their ability to carry out normal day-to-day activities. Five elements do the work — impairment, substantial, long-term, adverse effect, and normal day-to-day activities — and each one carries its own weight.

The word substantial is defined elsewhere in the Act as "more than minor or trivial". That is not a clinical threshold; it is a legal one, and it does not map onto any diagnostic category or severity score. A condition can be severe by medical standards and still require case-by-case analysis under the Act; a condition that is mild in clinical terms may still produce effects that clear the substantial bar. The phrase does not generate a count on its own.

Long-term is defined in Schedule 1 of the Act: the impairment has lasted at least twelve months, is likely to last at least twelve months, or is likely to last for the rest of the person's life. The twelve-month threshold is precise but applied prospectively — it asks about expected duration, not completed duration. A person newly diagnosed with a condition expected to last two years satisfies the long-term condition at the point of diagnosis, not a year later.

Normal day-to-day activities is deliberately undefined. The statutory guidance lists examples — mobility, manual dexterity, memory, ability to concentrate — but does not close the list. Specialist activities, notably those specific to a particular job, are excluded, which means the same impairment can be a disability for one purpose and require further analysis for another.

The parts that modify the definition

Schedule 1 of the Act contains several provisions that adjust who falls inside or outside the definition, and they matter for any count derived from the legal test.

Cancer, HIV infection and multiple sclerosis are deemed to be disabilities from the point of diagnosis, and other progressive conditions are covered from the point at which the impairment has any effect on normal day-to-day activities, even if that effect is not yet substantial. This deeming provision moves the threshold earlier in the course of a condition than the core definition would place it.

Severe disfigurement is treated as satisfying the substantial adverse effect condition without any further requirement to demonstrate effect on activities. Addictions to non-prescribed substances are explicitly excluded. Conditions listed in regulations — including hay fever, where it does not aggravate another condition — are also excluded.

Where a person uses medication or other measures to manage their condition, the effects are assessed as if those measures were not being taken. This is the deduced effects provision. Someone whose blood pressure is controlled by medication is assessed on the effects the condition would have without that control, not on the effects they actually experience day to day. The exception is corrected vision: spectacles and contact lenses are not removed from the equation. The deduced effects rule means the legal population is not the same as the population of people experiencing functional limitation right now, and any count based on the definition has to account for that.

Why the definition is hard to count

The legal test is applied case by case, not at a population level. There is no register of people who satisfy section 6, no central determination, and no periodic audit. A count of the disabled population under the legal definition therefore has to be derived from survey data, where the questions asked — about duration, severity and effect — are proxies for the statutory elements, not the elements themselves.

Those proxies vary between surveys, which is one reason why the wording decides the number. The legal test sets the conceptual boundary; the survey instrument decides who ends up on the right side of it in any published figure.

Threshold is an independent publication about disability statistics and governance. It is not an advice, advocacy or support service, and nothing on this site should be read as guidance on any individual's circumstances, entitlements or rights.