How RealSalary calculates your UK take-home pay
The order in which the calculation runs
The calculator follows the sequence a payroll system uses, because the order changes the answer. Pension contributions deducted under a net pay arrangement come off first and reduce taxable pay; deductions taken after tax do not.
Income Tax is then charged on what remains above the personal allowance, through the basic, higher and additional rate bands. The allowance itself is not fixed: above £100,000 it tapers away by £1 for every £2 of income, which produces an effective marginal rate of 60 % on that stretch of income. The calculator models the taper explicitly rather than applying a flat band, which is where simpler tools diverge most.
National Insurance is charged separately, on earnings between the primary threshold and the upper earnings limit at the main rate, and above the upper earnings limit at the reduced rate. It is assessed per pay period, not cumulatively, so the monthly figure is the authoritative one and the annual figure is its sum.
Student loan repayments, where selected, are a fixed percentage of income above the threshold for the relevant plan. Plans 1, 2, 4, 5 and the postgraduate loan have different thresholds and are charged in parallel where both apply.
Scotland is calculated separately
Income tax on earnings is devolved in Scotland, which uses its own bands and rates. National Insurance is not devolved and remains identical across the UK. Selecting Scotland changes only the income tax part of the calculation, and the calculator says so in the breakdown rather than silently applying different numbers.
What the calculator does not do
It does not model salary sacrifice, benefits in kind and the P11D, the Marriage Allowance, the High Income Child Benefit Charge, blind person's allowance, or tax codes other than the standard one. It assumes a single employment on a cumulative code.
It is an estimate for guidance. Your real deductions depend on the tax code HMRC has issued to your employer, and on adjustments carried over from previous years.
When the figures are updated
Rates and thresholds change at the start of the tax year on 6 April, and occasionally mid-year. We update after the rates are published by HMRC, not on the strength of Budget coverage. Each page shows the date of its last revision, taken from the site's version history.
Where the figures come from
Every rate and threshold is taken from the following official publications: