Calculation methodology

Every calculator on this site runs on one shared engine (v1.0.0) and one tax-year configuration, so two tools can never disagree about the same rate.

Order of operations

1. Annualise whatever you entered, using your hours and weeks where relevant.
2. Deduct pension contributions to reach taxable pay.
3. Work out the personal allowance, tapering it above £100,000.
4. Apply the income tax bands for your jurisdiction, slice by slice.
5. Apply National Insurance to the relevant earnings or profit.
6. Apply any student loan repayment above the plan threshold.
7. Deduct anything taken from net pay, then divide into periods.

Rates and sources

What we do not do

• We do not give tax advice, and we do not tell you what to do with your money.
• We do not model every relief, allowance or edge case — the limitations on each tool say what is excluded.
• We do not store the figures you enter. Calculations run in your browser.
• We do not rank commercial partners by how much they pay, and partnerships never change a result.

Commercial disclosure

Some links on this site are commercial partnerships. If you use them we may be paid a fee, at no cost to you. Partnerships never change how a calculator works or what a result says, and we do not rank partners by how much they pay.

Corrections

If a rate looks wrong, it matters more to us than anything else on the site. Rates are reviewed when HMRC and the Scottish Government publish changes, and each tool shows the review date it is running on.