About
effectivetax.co.uk is a free UK take-home calculator with a single focus: showing you your real marginal and effective tax rate, and the moves that lower it.
Its flagship is the "tax trap" between £100,000 and £125,140, where losing your Personal Allowance pushes your marginal rate above 60%. It is also where a pension contribution or a Gift Aid donation can claw that allowance back.
What it models
Income Tax for England, Wales, Northern Ireland and Scotland, and employee National Insurance. Pensions in all three forms, meaning net pay, salary sacrifice and relief at source, including the higher-rate relief you can reclaim. Student loans on every plan, benefits in kind, Gift Aid, bonuses and generic salary sacrifice. It uses the published rates for whichever tax year you select.
How accurate is it?
The calculation engine is checked against the HMRC PAYE estimator, matching it to the penny across more than 180 captured scenarios. Every figure the site shows comes straight from that verified engine.
Who maintains it
This site is built and maintained by a software engineer, not a large publisher or an advertiser. The figures are not opinion. Every rate and threshold is taken from HMRC and gov.uk, and the engine that produces the numbers is checked against the official HMRC estimator to the penny. The site shows no adverts and keeps your figures in your own browser, so nothing you enter is sold, shared, or even sent to a server.