About
Free UK pay, tax, pension and student loan calculators with their working shown and their sources listed.
What this is
Keepsum is a set of free calculators for people paid through PAYE in the UK: take-home pay, the £100k tax trap, student loan repayments, pension growth and a household view. There are no accounts, no sign-up and nothing to buy. The calculators are meant to answer the questions people actually ask of their payslip, in the words they ask them.
Who makes it
It is built and run by one person in the UK who got tired of calculators that were out of date, hid their working, or wanted an email address first. It is not a regulated firm and does not give financial advice; it shows what the published rules do to a given set of figures.
How the figures are kept right
Every rate and threshold lives in one rules file for the 2026/27 tax year. Each figure carries the official page it came from, a status and the date it was last checked against that page. All 34 figures are verified, most recently on 20 October 2026. The engine follows payroll's own conventions so that the result matches a payslip (NI and the student loan deduction to the penny, income tax within pence), and it is checked against a real 2026/27 payslip: National Insurance and the student loan to the penny, income tax within pence. How we calculate has the detail and every source.
What we do not do
We do not sell anything, take commission, or pass your figures to anyone. What you type stays in your browser; see the privacy page. We do not recommend products, providers or courses of action. If a decision turns on a figure here, check it with HMRC or a regulated adviser first.
Found a mistake?
Tell us. A wrong figure on a site like this matters, and a report with the salary, the tax code and the payslip line that disagrees is the fastest way to a fix. Contact.