Log
Changes and corrections
When a published number changes, it is recorded here with the reason. A site that silently edits its figures is not checkable.
29 August 2026 — first publication
Site built with the 2026/27 rates for England, Wales, Northern Ireland and Scotland, read from GOV.UK on 29 August 2026. See sources for each page and what it supplied.
One correction was made during construction, before publication, and is recorded because it changed a published figure: marginal rates were originally measured over a £1 step, which carried up to half a penny of penny-rounding and therefore half a percentage point of error. Scotland at £110,000 reported 70.0% against a hand-worked 69.5%. The step is now £100 and the same figure is exact. The method explains it.
When the rates change
UK income tax and National Insurance rates change at the start of the tax year on 6 April, and are usually announced at the preceding Budget. Scottish rates are set separately by the Scottish Government and announced at the Scottish Budget, typically in December. When they change, the parameter file changes, the whole site recomputes, and the change is recorded here.
What gets logged here
Three kinds of change are recorded on this page, with a date. A correction is a published figure that was wrong and is now right; those are logged whether or not anyone reported them and whether or not anyone would have noticed. A rate change is a statutory parameter moving, which normally happens at the start of a tax year and occasionally in-year; the old value and the new one are both recorded so that a figure someone quoted last month can still be explained. A scope change is the site starting or stopping modelling something.
Editorial and design changes are not logged, because they do not change an answer. Changes to the privacy notice, the terms or the funding disclosure are logged, because those are promises rather than opinions.
Why a public log rather than a quiet edit
A static site can be edited silently and completely: the old page simply stops existing, and unless someone kept a screenshot there is no evidence it ever said anything different. That is exactly why the log matters. A site that publishes numbers people act on — a salary negotiation, a pension contribution, a decision about a bonus — is asking to be trusted about the past as well as the present, and the only way to earn that is to make the past inspectable.
It also changes the incentives here. Knowing that a correction will be published, with a date and an explanation of what the wrong number was, is a strong reason to check the arithmetic before publishing rather than after. Two of the corrections recorded during construction were found precisely because writing the log entry forced the question "what would this have told a reader?" to be answered explicitly.
How to report something
Send it to corrections@taxwedge.com. The most useful report contains the page address, the figure the page showed, the figure you expected, and where your expected figure came from — a payslip, HMRC's estimator, or your own working. A disagreement with a payslip is not automatically an error here: the common causes are a tax code that is not the standard one, a benefit in kind, a salary-sacrifice pension deducted before tax, and National Insurance charged per pay period rather than annually, which makes a bonus month look worse than the annual figure. Those are worth ruling out first, but a report that turns out to be one of them is still welcome, because a page that fails to explain them is a page with a real problem.
Reports are answered. Corrections are published without naming the person who sent them unless they ask to be named.
Tax year boundaries
The UK tax year runs from 6 April to 5 April. Every page states the tax year its figures apply to, in the eyebrow above the heading and again in the assumptions. When the rates roll over, the change is logged here with both the old and the new value for each parameter that moved, and the pages are regenerated from the new parameters rather than edited by hand — which is why a rate change touches every page at once and cannot leave one family behind.
Corrections made before launch
Publishing these is unusual and deliberate. A corrections log that begins on launch day implies the site arrived correct, which no site does; recording what was wrong during construction is the more honest starting point and it sets the standard for what gets logged later.
Three are worth naming because each changed a number a reader would have seen. The marginal rate was originally probed over a one-pound step with penny rounding left on, which put up to half a percentage point of rounding noise on the answer — Scotland at £110,000 reported 70.0% against a hand-worked 69.5%. Separately, the "next change in your marginal rate" note on each salary page scanned the curve on a £100 grid, so it reported thresholds at grid points rather than at the real boundary: pages said the 62% band ended at £125,100 and the rate fell to 53%, when the answers are £125,140 and 47%, and the marginal-rate page linked from the same page said so correctly. And the share link on the calculator published the computed annual figure while labelling it an hourly rate, so a shared hourly result opened as a nine-figure salary for whoever received it.
All three had the same shape: code that was correct in one place and contradicted itself in another. That is why the engine is now the single source for every band figure on the site, and why the calculator and the pre-built pages are asserted to be running byte-identical code.
Versioning and archived figures
There is no version number on a page, and that is deliberate: a tax figure is identified by its tax year, which is stated on every page that computes one, and a version number would add a second identifier that could disagree with the first. When the rates roll over, the previous year's figures are not kept as a parallel site — the log records what changed, and HMRC's own archived rate pages remain the authoritative record of what applied when.
If you need to establish what this site said on a particular date — for a dispute, or because you acted on a figure — the log entry for the relevant change is the starting point, and corrections@taxwedge.com will answer specific questions about it.
What is not logged, and why that is a choice
Wording, layout, new pages and internal links are not recorded here. That is not laziness about transparency; it is an attempt to keep the log worth reading. A log that records every change records nothing useful, because the entries that matter — a number that was wrong, a rate that moved, a promise that changed — are buried among hundreds that do not. The test applied is simple: would this change give a reader a different answer, or break a commitment made to them? If neither, it does not appear.
The consequence is that this page will stay short for long stretches, and that is the intended behaviour rather than a sign it has been forgotten.
Contact for anything not covered here
General questions about the site, its method or its scope go to contact@taxwedge.com. Anything about a specific figure — including a suspicion rather than a certainty — is better sent to corrections@taxwedge.com, because that is the address that gets read against the arithmetic rather than against the prose.
A note on dates
Entries are dated by the day the change went live, not the day it was written or the day it was reported.