About KeenCalculator

What this is

KeenCalculator is a collection of 404 free calculators and converters for pay, money, math, health, dates, and home and car projects. Each one is a plain web page that loads instantly, works on a phone, and answers as you type.

How it is built

Every page is static HTML. There is no app framework to download and no server doing the arithmetic: the calculation runs in your browser. That is why results appear immediately and why the site keeps working on a slow connection.

Each calculator ships with worked examples. Those examples are also automated tests — every time the site is built, each one is recalculated and compared with its stated answer, and the build fails if any of them disagree.

What it remembers, and where

The site remembers your last inputs for each calculator, any setups you save by name, your calculators pinned to the home page, and a history of results. All of it is stored in your browser on your device. None of it is sent to us. You can export it as a backup file, import it on another device, or delete it from the History page.

Accuracy

Formulas are shown on every page so you can check them. Results are estimates for general information. For decisions about money, health, law or construction, confirm the numbers with a qualified professional and your local rules.

Found a mistake or want a calculator added? Write to hello@keencalculator.com.