How we check our calculators

Every calculator on this site is a working tool, not an article. Before any calculator goes live:

• Its formula comes from a named, linked source, shown on the page.
• It passes a set of test cases worked out by hand or taken from the source. Today the site runs 69 tests across 16 calculators, and a release is blocked if any one fails.
• The worked example on each page is produced by the same code you use, so the example and the calculator can never disagree.
• Each page shows the date its rules were last checked. Rules that change yearly, such as tax slabs, are re-checked on budget day.

Your numbers stay in your browser. The maths runs on your device, and nothing you type is sent to us or stored.

Found a mistake? That matters to us more than anything else here. A contact address is coming soon.