Why official figures change: how to understand revisions
Official statistics are revised when later or more complete data arrive, when methods improve, or when seasonal patterns are re-estimated. Revisions are planned and announced in advance, and the ONS publishes earlier estimates so you can see what changed. When a claim and a source disagree slightly, check whether one uses an earlier estimate.
Why figures are revised
Early estimates are published quickly so they are useful, but they rely on incomplete information. The ONS article Why GDP figures are revised explains how estimates are updated between monthly, quarterly and annual releases. The usual reasons are:
Late returns. Surveys keep receiving responses after the first estimate. The July 2026 monthly GDP bulletin reports a turnover response rate of 86.5% for the production part of the Monthly Business Survey in July 2026, compared with annual averages of 97.7% to 97.9% for 2023 to 2025.
Annual data. Detailed annual sources replace quarterly ones. In the UK national accounts this happens in the yearly Blue Book.
Seasonal adjustment. Each new data point changes the estimated seasonal pattern slightly; see seasonally adjusted .
Method changes , which are announced in advance.
Revisions follow published policies, such as the ONS National Accounts Revisions Policy . A revision is different from a correction of an error, which is also announced but is unplanned.
Sources: Why GDP figures are revised, National Accounts Revisions Policy
Worked example: UK GDP estimates during 2026
On 13 October 2026 we opened three ONS releases and compared what each said.
GDP first quarterly estimate, UK: January to March 2026 , released 14 May 2026: "GDP is estimated to have increased by an unrevised 1.4% annually in 2025, following revised growth of 1.0% in 2024 (previously 1.1%)." It also revised monthly growth for January and February 2026 down from 0.1% and 0.5% to zero and 0.4%.
GDP first quarterly estimate, UK: April to June 2026 , released 13 August 2026: GDP "increased by 0.4% in Quarter 2 (Apr to June) 2026". It states there were no revisions to earlier data in that release.
Quarterly national accounts, UK: April to June 2026 , released 30 September 2026: GDP "grew by 0.5% in Quarter 2 (Apr to June) 2026 (revised up by 0.1 percentage points from the previous estimate)", and "GDP for 2025 as a whole is estimated to have increased by 1.2%, revised down by 0.1 percentage points from the previous estimate."
So within a few months the published growth rate for the second quarter of 2026 moved from 0.4% to 0.5%, and annual growth for 2025 went from 1.4% in May to 1.2% by the end of September. Someone who said "growth was 0.4% in the second quarter" in late August was quoting the official figure of the day; the same sentence in October would be out of date.
The September release also says its data are consistent with Blue Book 2026, due on 30 October 2026, and the July monthly GDP bulletin says the whole series would be open for revision in the release of 15 October 2026. More movement was therefore expected.
Sources: GDP first quarterly estimate, UK: January to March 2026, GDP first quarterly estimate, UK: April to June 2026, Quarterly national accounts, UK: April to June 2026
How to see every earlier estimate
Real-time databases. The ONS publishes the real-time database for UK GDP (ABMI) , which keeps each vintage of the quarterly GDP volume series, and a matching one for GDP at current prices (YBHA).
Revisions triangles. The revisions triangles for monthly GDP show each estimate of each month's growth as it was published.
Previous releases. Every ONS bulletin has a "View previous releases" link. Dated URLs stay fixed, so you can open the release a speaker would have seen.
Sources: real-time database for UK GDP (ABMI), revisions triangles for monthly GDP
Revisions outside GDP
Population figures are also revised. The mid-2025 population bulletin (1 October 2026) says the ONS has "revised population estimates for mid-2022, mid-2023 and mid-2024 to use updated data for international migration", and notes that for Wales and Scotland "both the size and direction of population change may be revised" because the mid-2025 changes were small. Migration, earnings and many health series follow similar patterns: provisional figures are replaced by final ones.
Some measures are rarely revised by design. Check the revisions policy named in each bulletin's quality section.
Corrections are different from revisions
A correction fixes an error. The ONS states its corrections openly in the bulletin. The CPI bulletin for August 2026 , for example, reports "a minor error in the classification of several products in our scanner-based consumption segments from February 2026" and says the error "has no impact on published headline growth rates" for CPI, CPIH or RPI. Notices like this tell you which figures, if any, are affected.
When describing a changed figure, use neutral wording: "the ONS's first estimate was 0.4%; the latest estimate is 0.5%". A revision is a normal part of how estimates improve and not evidence that the earlier figure was wrongly reported.
Source: CPI bulletin for August 2026
How to handle revisions when checking a claim
Find the date the claim was made.
Open the release that was current on that date, using the "View previous releases" link.
Compare the claim with that release first. Then compare it with the latest release.
If both differ, describe it accurately: "the figure published at the time was X; it has since been revised to Y".
When comparing two periods, take both from the same release, so that revisions do not show up as a change that never happened.
Our method for checking a statistic includes this step, and how to read an ONS bulletin shows where each bulletin states what it has revised.
Checklist
Found the date the claim was made
Opened the release current on that date
Compared with the latest release
Read the bulletin's revisions note
Checked when the next scheduled revision is due
Took compared periods from the same release
Official sources used in this guide
Sources: ONS: Why GDP figures are revised, ONS: Quarterly national accounts, UK: April to June 2026, ONS: GDP first quarterly estimate, UK: April to June 2026, ONS: real-time database for UK GDP (ABMI), ONS: revisions triangles for monthly GDP, ONS: National Accounts Revisions Policy