How the number is built

Where a source can be read two ways

A single number in an international dataset does not carry its own meaning. The same field is a percentage of the tax due in one country, a contribution on gross in another and a levy on taxable income in a third. Rather than pick a reading and hope, every reading the data allows is computed in full, and the only one kept is a reading that reproduces the published outcome at all three income levels. Where none of them does, the jurisdiction is not published.

A rate is usable here only once it records the document it was read from, where in that document it sits, the date it was read, and how long it may be trusted before it is read again. A rate missing any of those is not incomplete data that renders anyway. It is data this site cannot compute with at all, so there is no path by which an unattributed figure reaches a page.

Each jurisdiction's calculation is checked against examples worked out separately from the calculator, and the two have to agree to the penny rather than to within a rounding margin. Amounts are held in whole pence and cents throughout, so a difference of one penny shows up as a difference instead of disappearing into a tolerance. Where a jurisdiction is withdrawn, its examples are kept with the reason attached and run again if it comes back.

Every rate is compared against a separately published compilation of the same law for the same tax year. Where the two disagree the disagreement is recorded against the rate and shown on the source of record rather than settled quietly in favour of whichever number was there first. A comparison that is settled by always preferring our own figure would tell you nothing, so it is recorded and left open instead.

What a salary page prints is checked against what the calculator produces for that salary. A page and the calculation behind it can drift apart while each looks correct on its own, and a reader has no way to see that from the page. This is the check that would notice.

Every rate carries a date by which it has to be read again. Once a page computes with a rate past that date, that page is not published. A tax figure does not announce that it has gone out of date, and a site with no expiry on its rates keeps serving last year’s numbers under a badge that still reads current.

A page has to carry a single top-level heading, headings that nest in order, its own permanent address, a description of itself, and enough substance to answer the question in its title rather than pointing somewhere else. Where a page shows a set of questions and answers, those are marked up as questions and answers so a search result quoting one quotes it correctly.

Pages of the same kind are measured against each other twice: once for two pages that have become substantially the same page, and once for a block of text repeated across the whole set, which comparing pages in pairs hides when every one of them carries it. A calculator with four hundred salary pages that says the same thing on each is not four hundred answers to four hundred questions.

Every page is rendered in full before it is published, and the rendered result is what gets served. The headings, the paragraphs and the numbers are present in the page as it arrives, so nothing here depends on scripts finishing before the page says anything.

Usain Olivard

Not a qualified tax adviser, and no such claim is made. The most recent figure behind this site was read from its source on 08 September 2026, which is the date this page reports as its last modification. Everything here can be checked against the document it came from without asking us anything.

More on who this is for and how it stays free is on the about page. The guides that use these figures are here. Ruleset sha256:fe993d9d072cbcac.