Eleven calculators, one engine

Every calculator here exists because the demand for it was measured before it was built, and each answers something the take-home figure alone cannot.

Why eleven rather than one

A single calculator with enough options can answer all of these questions, and that is exactly the problem: an interface with eleven modes asks you to know which mode you want before it will help you. People do not arrive wondering about "tax"; they arrive wondering whether the rise is worth it, what the bonus will land as, or what a hire really costs. Each page here is one of those questions with the controls it needs and none of the ones it does not.

They all run the same engine, so the answers are consistent by construction rather than by discipline. The engine file your browser downloads is byte-identical to the one that generated every pre-built page on this site, and a test asserts it — two implementations of a tax rule is one too many, and the drift between them shows up as a calculator disagreeing with the page it sits on.

What every one of them shows that most calculators do not

Two things. The rate on your next £100, which is the number every decision turns on and is routinely twenty points away from the effective rate on the same pay. And the employer's National Insurance — money spent to employ you that appears on no payslip in the country, and whose omission makes the burden on a job look about a third smaller than it is.

Nothing you type is sent anywhere. There is no server to send it to: these are static files, and the arithmetic runs in your browser using a rates file the page already downloaded. You can confirm that in the network tab of any browser in about ten seconds.

Both UK tax regimes, everywhere

Every calculator here carries a jurisdiction control, because income tax is devolved and a UK answer that ignores Scotland is wrong for about one worker in eleven. The Scottish figures use Scotland's own six bands over the UK-wide personal allowance, with UK-wide National Insurance on top.

They work without JavaScript

Every one of these pages renders a complete worked example on the server before any script runs, so the page answers its question even with scripting disabled or blocked. The controls then make that answer movable rather than creating it. That ordering is deliberate: a calculator that shows an empty box until a script loads is a page that fails silently for anyone on a restricted network.

Every answer is a link

Each calculator writes what you typed into the address bar, so the result you are looking at has its own URL. That makes an answer shareable, bookmarkable and reproducible — send it to a partner, keep it for a negotiation, or come back to it next month and get the same figure. Nothing is stored to make that work; the figure is in the link itself, which is also worth knowing before pasting one into a group chat.

What none of them model

All of them assume a single employment taxed through PAYE on the standard code, with employment income only. They do not know about benefits in kind, a tax code carrying an adjustment, more than one job at once, dividend or savings income, or anything assessed through self assessment. They also leave out the benefit cliffs and the Universal Credit taper, which produce marginal rates well above anything shown here but depend on household circumstances a salary box cannot ask about. Every page lists its assumptions where the figures are, not in a footnote.

What these do that a take-home figure cannot

A take-home number answers "what have I got". Every calculator here answers a question about a decision, and decisions are priced at the margin rather than the average. Is this rise worth taking? What does the bonus actually land as? What does a pension contribution cost me, in spending power, per pound that reaches the pot? What does this hire really cost? Those all turn on the rate on the next pound, which is a different number from the one on your payslip — often by twenty points or more.

They also each show the half of the arithmetic that is normally missing. Employer National Insurance is 15% of everything above £5,000, it is spent on employing you, and it appears on no payslip in the country. Leaving it out makes the burden on a job look about a third smaller than it is, which is why every tool here carries it.

What none of them model

All of these assume a single employment taxed through PAYE on the standard code, with employment income only. They do not know about benefits in kind, a tax code carrying an adjustment, more than one job at once, or income that is not a salary. They also leave out the benefit cliffs — the High Income Child Benefit Charge, and the England free childcare hours that stop dead at £100,000 rather than tapering — because those depend on household circumstances a salary box cannot ask about, and folding them in would produce a number that looked authoritative and was wrong for most readers.

Where those matter, they are explained in the guides instead, which is the honest place for something the arithmetic cannot settle.

Why they all agree with each other

There is one tax engine on this site and every page and every calculator imports it — the build asserts that the file shipped to your browser is byte-identical to the one that rendered the pages. Two calculators on the same site disagreeing about the same salary is a common and entirely avoidable failure, and this is how it is avoided. The method →