About Numbers Plainly
Free calculators that show their working.
What we do
Numbers Plainly is a collection of free calculators for money, health and everyday questions. We built it because many calculator sites give a number with no explanation, leaving you to trust it blindly. Every tool here shows the formula it uses, works through an example by hand, and lists the assumptions behind the answer.
How we make sure the maths is right
The calculation code lives in separate JavaScript files and is covered by an automated test script that checks results against hand-calculated values, round trips (for example converting a unit there and back), and edge cases such as a zero interest rate or invalid dates. When we find a mistake, we fix it and add a test so it cannot return.
Privacy by design
Calculations happen in your browser. The numbers you enter are not uploaded to our servers. Read our Privacy Policy for details about cookies and advertising.
How the site is funded
The site is free to use and is supported by advertising. Ads are clearly labelled and kept away from the input fields and buttons so they do not get in the way of using a calculator.
Limits you should know about
We aim for accuracy, but a general calculator cannot know your lender’s fees, your tax situation or your medical history. Please treat results as estimates and read the disclaimer. If you spot an error or have a suggestion, get in touch.