How big is the UK population, and how do we know?

The mid-year population estimate combines the census with registered births, deaths and migration to estimate usual residents of the UK each year.

What it measures

The mid-year estimate counts people usually resident in the UK — those living or intending to live here for 12 months or more — at 30 June each year, by age and sex.

How it is compiled

The ONS rolls the census forward using registered births and deaths and its migration estimates, reconciling with the next census when it lands. Scotland and Northern Ireland's statistical agencies produce their own estimates on the same basis, combined into the UK total.

What it is not

It is not a live count — estimates are published about a year in arrears and revised after each census. The country-of-birth split on this site comes from the 2021 Census for England and Wales, because the devolved censuses run on their own schedules.

Methodology

ONS population estimates methodology

UKStats reproduces the published figure exactly; the publisher's own methodology notes are the authoritative description of how it is compiled.