How we calculate

Data sources

All tax rates, thresholds, and allowances come from official UK government publications:

• Income tax — HMRC and the Scottish Government Budget. Rates are updated each April and stored in a central data file — they are never hardcoded into individual calculator pages.
• National Insurance — HMRC Class 1 primary thresholds and rates.
• Stamp Duty (SDLT) — HMRC. LBTT — Revenue Scotland. Both are updated after each relevant Budget announcement.
• ISA allowances — HMRC. Lifetime ISA bonus rules from government guidance.
• National Minimum Wage — Low Pay Commission annual recommendations, confirmed by BEIS.
• Student loan repayment thresholds — Student Loans Company / DfE for each plan type.

Scotland vs the rest of the UK

Income tax is devolved to Scotland. The Scottish Parliament sets its own rates and bands, which have been different from England, Wales, and Northern Ireland since 2017. Our income-tax and take-home pay calculators handle both sets of rates. Where relevant, a Scotland toggle or separate Scottish calculator is provided.

Property transaction tax is also different: Scotland uses Land and Buildings Transaction Tax (LBTT), not Stamp Duty Land Tax (SDLT). Our stamp duty calculator covers both, with a Scotland/England toggle.

National Insurance, ISA allowances, and student loan repayment rules are UK-wide and identical across all four nations.

What the figures include and exclude

Our calculators give accurate annual estimates based on current rates and thresholds. They are not payroll engines. A real payslip may differ slightly because:

• Your employer uses a period-by-period calculation with a specific tax code, not an annual one.
• Tax codes can vary from the standard 1257L — a different code changes how your Personal Allowance is applied.
• Mid-year pay changes, bonuses, and one-off payments are not modelled.
• Some pension schemes have specific rules around how contributions are calculated.

Treat our results as a close annual guide, not a certified payroll statement.

When rates are updated

We update all rates in April each year when the new tax year begins. The UK government occasionally announces mid-year changes (typically at the Autumn Statement or emergency Budgets) — we update within a few days of confirmed announcements.

Every calculator page shows a "last updated" date at the foot of the page. If you notice a figure that looks wrong, please let us know.