How many Muslims lived in the UK in 2021 and what are projections for 2025?

1. The 2021 baseline: “just under four million” in official counts

The most robust public anchor is the 2021 census outcome and downstream reporting: England and Wales recorded 3,868,133 people identifying as Muslim, Scotland’s separate 2022 census added 119,872, and Northern Ireland recorded 10,870 — together amounting to a UK total that census reporting and summaries describe as “just under four million” and about 6% of the population ^[1]. The Muslim Council of Britain’s census summary also presents a rounded figure of 4.0 million when discussing national context, drawing on Office for National Statistics and devolved agency data ^{[3] [5]}.

2. Minor differences in reportage: 3.9 vs 4.0 million and why they appear

Different outlets and briefings use slightly different roundings: independent summaries and some secondary sources report about 3.9 million in 2021, while organisational summaries and infographics round up to 4.0 million ^{[2] [3]}. These small discrepancies stem from whether one consolidates England & Wales, Scotland and Northern Ireland exact tallies, or presents a headline rounded figure; the underlying census tables remain the primary source ^{[1] [5]}.

3. Short-term outlook to 2025: conservative extrapolations and scenario projections

Simple, conservative extensions of observed inter-census growth (2001→2011→2021) produce modest increases and would place the 2025 Muslim population close to the 2021 figure — roughly in the high 3.9–4.1 million range if migration patterns and fertility trends do not change markedly, a position reflected in cautious estimates reproduced in analytical guides and data summaries ^[2]. By contrast, a cohort-component modelling exercise cited by an independent research centre projects the Muslim share of the UK population rising to 7% by 2025, which — depending on the assumed total UK population size used in that model — implies a noticeably larger headcount than the conservative extrapolation ^[4].

4. Why projections diverge: methods, assumptions and agendas

Divergence between conservative extrapolations and model-driven projections is methodological: short-run estimates often extend recent census growth rates forward and flag sensitivity to migration and fertility assumptions ^[2], while longer-run demographic models apply age-specific fertility, mortality and migration matrices to a 2022 base and can produce materially different percentages for 2025 depending on those inputs ^[4]. Institutional aims also shape presentation: community organisations summarise census totals to highlight current needs and parity issues ^{[5] [3]}, whereas academic or policy models may stress future trajectories and policy implications, which can look alarming if assumptions skew toward higher migration or slower fertility convergence ^[4].

5. What can be stated with confidence — and what remains uncertain

It is certain, based on census data and official summaries, that around 3.9–4.0 million people in the UK identified as Muslim in 2021, making Islam the second-largest religion by adherents in the country ^{[1] [3]}. Estimates for 2025 are not uniform: conservative data-driven estimates keep the total near that 2021 baseline ^[2], while at least one projection model forecasts a Muslim share of about 7% in 2025, which would translate into a higher headcount depending on overall population size assumptions ^[4]. Sources do not present a single agreed numeric forecast for 2025; readers must weigh the underlying assumptions — migration, fertility convergence, and ageing — when interpreting competing figures ^{[2] [4]}.