Percentage Calculator

How it works

To find a percentage of a number, convert the percentage to a decimal fraction by dividing by 100, then multiply by the base value. A percentage greater than 100 is valid and produces a result larger than the base when both values are positive. Negative numbers are accepted in this mode because the arithmetic is defined; the meaning depends on your context.

To compare an original and a new value, subtract original from new and divide the difference by original. Multiply by 100 to express that relative change as a percentage. This calculator requires a positive original value in change mode. Percentage changes from zero are undefined, and comparisons involving negative starting values can be misleading, so they are deliberately rejected.

Percentage change differs from percentage-point change. Moving from 20% to 25% is an increase of five percentage points and a relative increase of 25%. The direction of comparison matters too: increasing 100 to 120 is a 20% rise, but returning from 120 to 100 is a 16.67% fall. Results use standard browser floating-point arithmetic and are rounded to eight decimal places for display. For accounting or contractual work, apply the rounding convention your context requires.

A worked example

15% of 200 equals 30. An increase from 200 to 250 is (250 − 200) ÷ 200 × 100 = 25%. A decrease from 250 to 200 is 20%, because the original value has changed.

Common questions