About PercentageCalcs
How the calculators work, how answers are checked, and how to report a problem.
Last updated November 9, 2026
A calculator you can check
PercentageCalcs is a free collection of percentage calculators for everyday arithmetic, grades, sport and science. Each calculator shows its formula with your numbers substituted so you can check the answer. No account is required.
The site maintainer receives corrections and suggestions through the feedback form. Include the calculator name, inputs, expected answer and the source or method you used. You do not need to include personal information.
Methods and conventions
- Percentage change: (new − old) ÷ |old| × 100. Using the magnitude of a negative starting value is a convention, not a universal financial reporting standard. A starting value of zero has no defined percentage change.
- Percent difference: compares the gap between two values with their average. It answers a different question from change over time.
- Percentiles: use linear interpolation. Other percentile definitions can produce different answers on small datasets.
- Grades: the score percentage is independent of school policy. The optional American letter-grade scale is an example, not a universal grading standard. The target tool rounds up to a whole mark.
- Win percentage: ties count as half a win. The target tool assumes every future game is a win. League points systems may use other rules.
Precision and checking
Calculations use JavaScript number arithmetic. The math engine rounds results to 12 significant digits to remove common floating-point noise. Displayed answers can use fewer decimal places for readability; rounding can matter for very small or very large values.
Automated tests cover the core formulas, zero denominators, decimal input, negative values and target calculations. Build checks also compare translated examples with the English source. These checks help catch mistakes but do not replace an independent review for consequential decisions.
Your numbers and shared links
Editing a calculator runs the arithmetic in your browser. Copy answer creates text you can paste elsewhere. Share calculation creates a link containing the inputs; anyone with that link can read them. Opening a shared link sends its URL to the site and may expose it to browser history, server logs and analytics. Avoid sharing confidential numbers.
See the privacy policy for analytics and feedback details. Batch exports are generated on your device.