About TaxCliff

Fatih Bilgiç — Software engineer. Built and maintains this site. Not a tax adviser — which is why every figure names its source and every calculation shows its arithmetic. You can find my other work at antagrioin.com/fatih-bilgic/.

This is run by one person, not a company. I mention that because a finance site with no visible operator is one you have no reason to trust, and I would rather tell you exactly how small it is than let the design imply otherwise.

Every calculation on this site can be opened up. Under each result is the arithmetic, step by step, with the rule that was applied and a link to the page it is published on. If a figure cannot be traced to a primary source, it does not appear as a number anywhere — it appears in the not confirmed list instead.

That is a deliberately awkward commitment. It means the site sometimes says "we could not confirm this" where a competitor prints a confident figure. We think that is the right trade in a subject where being wrong costs the reader money.

This is an information tool, not financial advice. It does not know your circumstances, it cannot see your tax code, and it will not tell you what to do. For a decision that matters, talk to a qualified adviser.

It also is not a payslip. Employers operate PAYE on a cumulative, per-period basis with your actual tax code; this site works on an annual basis with standard assumptions. Those agree for a steady salary and diverge for irregular pay — the methodology page is explicit about where.

Every rate and threshold is read from a primary source — a gov.uk page, a gov.scot page, or the legislation itself — and then read a second time, independently, by someone trying to prove the first reading wrong. Where the two disagree, the second reading wins. Both the URL and the sentence the figure was taken from are stored alongside the number and shipped to the page, which is why the working under any result can link straight to the source.

That process has already caught things worth catching. The National Insurance exemption on salary-sacrificed pension contributions is being capped by an Act that received Royal Assent in April 2026 — but the commencement provisions delay it to the 2029-30 tax year. Applying it now, which a calculator working from memory would do, would understate take-home pay for everyone using salary sacrifice.

The calculations themselves are covered by a test suite that runs before anything is published. Some of those tests assert properties that should hold whatever the rates are; others pin specific figures worked out by hand, and exist precisely so that a rate change breaks the build loudly instead of quietly moving everyone's answer.