How the National Insurance Calculator works
This tool estimates UK employee National Insurance (Class 1) — the contribution deducted from your pay alongside Income Tax. It uses the standard banded formula HMRC applies to earnings above the primary threshold, so you can see how much NI comes out of a given salary, and how much of the deduction sits in the main-rate band versus the additional-rate band.
The formula
Annual gross pay is split into three bands relative to the primary threshold (PT) and the upper earnings limit (UEL):
- Pay at or below the PT: 0% NI
- Pay between the PT and the UEL: charged at the main rate (8% by default)
- Pay above the UEL: charged at the lower additional rate (2% by default)
As an equation: NI = (min(pay, UEL) − PT) × main rate + max(pay − UEL, 0) × additional rate, with the result set to zero whenever pay is at or below the PT. The default thresholds (£12,570 PT and £50,270 UEL) and rates (8% and 2%) reflect employee NI for a standard category-A employee; all four fields are editable so you can model an earlier tax year or a different NI category.
Worked example
Take a £35,000 annual salary. The first £12,570 is NI-free. The remaining £22,430 (£35,000 − £12,570) falls entirely within the main-rate band because it's below the £50,270 upper earnings limit, so NI is £22,430 × 8% = £1,794.40 a year, or about £149.53 a month and £34.51 a week. On a higher salary of £60,000, the main-rate band contributes (£50,270 − £12,570) × 8% = £3,016.00, and the additional-rate band adds (£60,000 − £50,270) × 2% = £194.60, for a total of £3,210.60 a year.
What moves your NI bill most
- Gross pay relative to the thresholds: earnings near or below the primary threshold owe little or no NI; earnings well above the upper earnings limit pay a growing share at the main rate before the cheaper additional rate kicks in.
- The main rate: because most employees' taxable pay sits in the PT-to-UEL band, changes to the main rate have the largest effect on take-home pay for typical salaries.
- The additional rate: this only affects pay above the upper earnings limit, so it matters most for higher earners.
What this calculator does not cover
This is an employee (Class 1) estimate only. It does not calculate employer secondary Class 1 contributions (which use a different secondary threshold and rate and are paid by the employer, not deducted from your pay), and it does not calculate Class 2 or Class 4 National Insurance for the self-employed, which use separate profit-based thresholds. National Insurance is also normally worked out per pay period rather than by simply dividing an annual total, so if your income is irregular or you hold multiple jobs, your actual payslip figure may differ slightly from this estimate. This tool provides an estimate for planning purposes and is not a substitute for payroll software or professional tax advice.