Check the formula
Calculator pages explain the formula or logic behind the result in plain English. For everyday maths, that may be enough. For tax, health, borrowing and other important decisions, check the source links and assumptions too.
Read the assumptions
A result is only as good as the assumptions behind it. Mortgage payments can exclude fees. Salary estimates can miss tax code details. Health calculators can estimate a range, but they cannot know your full medical context.
Use source links where rules change
Pages that depend on changing thresholds, rates or public guidance include source links where practical. Always use official or professional advice before making a high-impact decision.