About CalcNinja

What we do

CalcNinja publishes free calculators for health, finance, maths, unit conversion and everyday tasks. Each one is designed to load fast, work on a phone, and show the formula behind the answer so you can check the result yourself.

There is nothing to install and no account to create. Open a calculator, type your numbers, and get an answer.

How our calculators work

Every calculation runs in your own browser. Nothing you type is sent to a server, logged or stored, which means your figures stay on your device.

We publish the formula and a worked example alongside each calculator so you can see exactly how a result was reached, and reproduce it by hand if you want to.

Accuracy

We use standard, published formulas and full double-precision arithmetic, rounding only for display. Where a formula has more than one accepted variant, we say which one we use.

Our tools are for general information. They are not a substitute for advice from a doctor, accountant or other qualified professional.

Get in touch

Found a mistake, or want a calculator we do not have yet? Tell us on the contact page. Corrections are the fastest way to make the site better for everyone.