About acalculator

acalculator is a set of free online calculators for big decisions and small curiosities: loans and savings, health, maths, dates, construction, and more. There is no sign-up.

How the answers are checked

Each calculator comes from a published formula or a hand calculation. Its worked examples run as tests on every build, and a second, independent implementation checks it with random inputs. The page shows the formula, the assumptions, and the worked examples, so you can check the answer yourself.

How the pages work

The calculations run in your browser as you type. Nothing you type is sent to a server. Each page also has plain Markdown and JSON copies for software that reads the site.