Math Calculators

These math calculators cover the everyday arithmetic that comes up in homework, shopping, cooking and work: percentages, ratios, proportions and number problems. Every calculator shows its working with your numbers, so you can check the answer by hand or copy the method for a worksheet.

Each page also explains the formula in plain words, with worked examples and answers to common questions. If you're not sure which one you need: a percentage compares a part to a whole out of 100, a ratio compares two amounts to each other, and a proportion says two ratios are equal, which lets you find a missing number.

All math calculators

Percentage CalculatorPercent of a number, percent change, and increase or decrease by a percent.
Proportion CalculatorSolve A/B = C/D for the missing number, with steps.
Ratio CalculatorSimplify ratios, convert to 1:n, and split a total in a ratio.

Key formulas

Percent of a number: P% of X = P ÷ 100 × X Percent change: (new − old) ÷ |old| × 100 Proportion: A / B = C / D → A × D = B × C Simplify a ratio: divide every part by their greatest common factor