Where the rules come from
Tax bands, end-of-service rules and other legal figures are taken from the law itself or the government body that publishes it, such as a Finance Act or a country's labour law. Where official sources are unclear or courts disagree, the calculator says so and lets you choose, rather than picking one answer silently.
Health calculators use published formulas, for example Mifflin-St Jeor for calories and the US Navy method for body fat, with the formula shown on the page.
How each calculator is tested
- The worked example on every page is run through the calculator in automated tests, so the page and the tool can't disagree.
- Results are checked against hand calculations and known reference values, including edge cases such as leap years, month ends and part years of service.
- Every page is checked on a phone-sized screen before it goes live.
Keeping rules current
Each page that depends on a law or rate shows the date we last checked it. We review tax and salary rules when a new budget or law takes effect, and update the page and its date.
Estimates, not advice
Our results are estimates to help you understand and plan. They are not financial, legal, tax or medical advice. For a decision that matters, such as a tax filing, a dispute with an employer or a health concern, check with a qualified professional.
Advertising does not affect results
CalcPenguin is free and may be paid for by advertising. Advertisers have no say in what our calculators show.
Corrections
If you think a result is wrong, use the “report a problem” link on the calculator or email hello@calcpenguin.com. A share link with your inputs helps us check it quickly. We fix confirmed mistakes promptly and update the page's last-checked date.
Last updated 25 October 2026.