Methodology
How the UK figures are selected, calculated, compared and kept auditable.
One site, separate statistical systems
UK data are kept in a separate country namespace and API. U.S. foreign-born status is defined by citizenship at birth; UK non-UK-born data use birthplace. Similar labels do not make those measures directly comparable.
Source selection & audit trail
This release uses ONS, Nomis and Home Office publications. Every metric has a definition, formula, population, date, unit and source. Original XLSX, ZIP/CSV and HTML bytes are preserved with SHA-256 hashes. The HTML snapshot downloads as plain text. Data are cached in the application release and reviewed before database publication.
Flows, stocks and administrative events
ONS migration estimates measure moves lasting at least 12 months. Census population is a stock of usual residents on one day. Visa grants are administrative decisions and include dependants where specified. Asylum claims, decisions and pending cases are different cohorts. These categories must not be summed to count immigrants.
Dates and geographic coverage
Migration charts use years ending December. Current Home Office headlines cover the year ending June 2026; pending asylum figures describe 30 June 2026. Census data cover England and Wales on 21 March 2021. The separate modelled non-UK-born population series covers the UK in mid-2022 to mid-2024. Scotland and Northern Ireland regional data are not inferred from other places.
Historical comparability
The May 2026 ONS migration release supplies one consistent source version for the displayed historical series. British and EU+ estimation methods change from year ending June 2021. Trend lines do not bridge that break. Earlier values remain available with this caveat. Nationality-group definitions also change across the series.
Rounding and calculations
ONS and Home Office headline values are rounded to the precision published. Net migration is ONS's published difference calculated before rounding; the rounded immigration and emigration figures can differ from it by 1,000. Census non-UK-born count is TS004 total minus UK-born count, and share divides that difference by the same table's total. Percentage change uses (current − prior) ÷ prior × 100 and is unavailable with a missing or zero baseline.
Uncertainty, missing data and revisions
ONS migration estimates are official statistics in development. 2025 is provisional. Table 2's 95% simulation intervals appear in metric tables where supplied; they may understate uncertainty and do not cover all sources of error. No intervals are invented for other data. Missing values are absent or N/A, never zero. Source versions and observation revisions are retained; new releases require review.
Census country rankings
TS012 rankings include separately named overseas countries and territories, excluding UK-born categories and residual regional groups. TS004 and TS012 can differ because of disclosure control. No citizenship or legal-status category is inferred from birthplace.
Border, asylum, crime and fraud
Detected irregular arrivals are not the resident population without immigration permission. Small-boat arrivals are a subset of detected arrivals. Returns include voluntary and enforced processes. Asylum refusal is not fraud. Crime, fraud, fiscal and housing datasets are outside this UK release; none are inferred from ethnicity, birthplace or nationality.
Release coverage & next imports
This is an initial UK section. Employer-level visa use, detailed Skilled Worker statistics, occupations, wages, regional time series, Scotland and Northern Ireland census tables, and comprehensive refugee data await source review. Home Office headline histories are not reconstructed from published percentage changes. New releases are checked through a scheduled review workflow; publication follows validation. See Data updates for its scope and limitations.