Methodology
Each calculator comes from one verified record: inputs, formula, sources and the date checked. Compute tests run at build time and every page keeps a changelog.
Every page on this site is generated from a single JSON record. For a calculator that record holds the input fields, the JavaScript formula, worked test cases, the method, a reference table, FAQs, the sources and the date the figures were checked.
At build time the formula is compiled and every test is run in Node. A record that does not compile, returns an invalid result or fails a test stops the build — it cannot reach a page.
Rates that move (tax slabs, electricity tariffs, fuel prices, MSP, DA, market rates) are exposed as inputs with a sourced default, so you can put in the number that applies to you. Where a number cannot be verified it is not published. Spotted an error? The page changelog records corrections; use the link in the page trust box to report one.