How our calculators work

Calculations run from the values entered by the user. A tool may apply arithmetic formulas, bands, rule-based questions or illustrative assumptions. Results are rounded for readability and can differ from official calculations that use more detailed information.

A time-sensitive tool should identify the tax year, effective date or rule version it uses and the UK nation it covers. England-only rules must not be presented as UK-wide. When rules vary by council, lender, provider or personal circumstances, the result should say so.

A result is not approval, eligibility confirmation, a diagnosis, a legal opinion or a regulated recommendation. Official bodies and qualified professionals may consider facts the tool does not collect.

Calculator changes should be tested against worked examples, boundary values and invalid inputs. A visible review date should be added only after the formula and supporting content have been meaningfully checked. Methodology or rate changes should be recorded on the relevant page.

If a result appears wrong, check the entered values and the assumptions shown on the page. Report a reproducible example through the contact page; do not include sensitive medical, financial or identity documents.