About Calclulo

Calculators that show their working.

Calclulo is a set of 136 free calculators for money, farming, science, health, school and daily life. Each one shows the formula behind its answer, so you can check the result instead of taking it on trust.

Why it exists

Most calculators hand you a number and stop there. You can't tell which formula it used, where it rounded, or what rate it quietly assumed. That matters when the number is a loan payment, a tax bill or the amount of seed to buy.

So every calculator here lists its inputs, states its assumptions, and comes with a worked example you can repeat by hand. The article underneath explains the idea behind the sum and the mistakes people usually make.

On every calculator page

• Inputs with short notes and defaults you can change.
• The result, the formula, and the other figures that come out of the same calculation.
• Copy and export buttons for keeping or sending the answer.
• A worked example, a written guide and common questions.
• Links to the official source where a rate, rule or health figure comes from an outside body.

Estimates, not advice

Rates and rules change: tax bands, customs duties, platform requirements. Where that applies, the page says which figures it uses, and you should confirm them with the official source before acting. The health calculators help you understand your numbers and cannot diagnose anything. The finance calculators are not financial advice. The tools for creators ask you to type in your own rate, because nobody can promise what a thousand views will pay.

If you find a wrong figure or a result that looks off, email us with the values you entered and the answer you expected. That is the quickest way for us to reproduce and fix it.

Your numbers stay with you

The maths runs in your browser, so what you type is not sent to us. There are no accounts or sign-ins. Once a page has loaded it works offline, and you can install Calclulo on your phone or computer. The details are in the privacy policy and the cookie policy.

Who makes it

Calclulo is a library of calculators. We want the pages accurate, written in plain language, and quick to load on an ordinary phone.

Get in touch

Missing a calculator? Use the contact page and describe the job you're trying to get done. That helps us build the right tool and not just another copy of one that exists. You can browse everything from the home page.