About PercentBase
A small, independent set of calculators built around one idea: show the working.
Why this site exists
Most online calculators give you a number and nothing else. That is fine the first time, and useless the tenth, because you learn nothing and you have no way to check whether you asked the right question. PercentBase was built the other way round. Every result comes with the formula that produced it and a step-by-step breakdown, so you can follow the method, spot your own mistakes, and eventually stop needing the calculator at all.
Percentages are the arithmetic people meet most often after basic counting — in shops, on payslips, in report cards, on invoices, in every news story about prices. They are also easy to get subtly wrong in ways that cost real money. A site that explains as it calculates seemed worth building.
What we believe about tools
- Fast is a feature. Pages are plain HTML, CSS and JavaScript with no frameworks and no trackers, so they open instantly even on a weak connection.
- Your numbers are yours. Every calculation runs inside your own browser. Nothing you type is transmitted to us or stored on any server.
- Explain, do not just answer. Formulas, worked examples and common mistakes sit on every page, written in plain English rather than textbook notation.
- Respect the reader. No pop-ups over the calculator, no newsletter interruptions, no ads disguised as buttons.
How the calculators are checked
Every formula on this site is covered by an automated test suite that runs the exact JavaScript file the website uses. Those tests cover whole numbers, decimals, zero values, very large values, negative values, empty input and division-by-zero cases. A change to a calculator does not ship until the full suite passes, and the current results are published in the project's testing report.
That said, no software is perfect. If a result ever looks wrong to you, please tell us — a reproducible example is worth a great deal.
How the site is funded
PercentBase is free to use and supported by advertising. Ads are kept in clearly marked areas, away from the calculator controls and the results, and are never styled to look like part of the tool. We would rather earn less than make the site annoying to use.
What is coming next
The current set covers the percentage questions people ask most. Planned additions include compound interest, a weighted grade calculator covering several assessments, ratio and proportion tools, and printable reference tables. If there is a calculator you keep wishing existed, tell us about it.
Contact
Corrections, feature requests and bug reports are all welcome through the contact page.