About PercentageTools
Focused calculators with visible formulas
PercentageTools is a collection of free, focused calculators for common percentage questions. Each calculator is built around one clear intent and shows the formula, result, and a worked example so the calculation can be checked instead of treated as a black box.
What the site provides
- Focused tools for percentage, change, difference, money, grade, and business questions.
- Plain-language formulas and worked examples beside the calculator.
- Related calculators when a question uses a different reference or comparison method.
- With JavaScript enabled, calculations run in the browser without an account or a separate calculation API.
What the site does not replace
PercentageTools provides general calculations, not professional financial, tax, payroll, academic, legal, or investment advice. Rules and rounding requirements can differ by institution, employer, jurisdiction, or use case, so important decisions should be checked against the relevant official guidance.
How results are checked
Formula, implementation, examples, and edge cases are reviewed together
The calculation process covers more than the number shown in the result box. It also checks that the implementation follows the stated formula, examples match the calculator, invalid inputs are handled clearly, and production pages keep their canonical and indexing signals.
Read the calculation methodology