Methodology & Sources

Source authorities

All tax rules, bands, thresholds, and National Insurance rates used across UKTaxTools calculators come directly from HMRC and GOV.UK. Scottish income tax rates come from the Scottish Government's published bands.

Update cadence

We review calculators at the start of each tax year (6 April) and again whenever HMRC publishes rate or threshold changes — typically following the Autumn Budget and Spring Statement. Every calculator page shows its own "Last updated" date, sourced from the file's last git commit.

Where the math lives

Calculation logic lives in tested TypeScript files under src/utils/, separated from UI, so every number shown can be traced back to a tested function.

Handling ambiguous rules

Where HMRC guidance is ambiguous or depends on personal circumstances we can't observe (residency, allowances transferred, marginal relief edge cases), calculators use the most common interpretation and flag the assumption inline.

Not financial advice

UKTaxTools provides general information only. It is not tax, legal, or financial advice. For a binding answer, speak to a qualified accountant or tax adviser.