Percentage change calculator

How percentage change works

Take the old value away from the new value, divide by the old value, and multiply by 100. From 80 to 100 the difference is 20, and 20 ÷ 80 = 0.25, so the rise is 25%. From 100 down to 80 the difference is −20, and −20 ÷ 100 = −0.2, a 20% decrease.

The two answers are different because each percentage is measured against its own starting point. A price that rises 25% and then falls 20% is back where it began.

Which number is "old"?

Always the one you are measuring from: last year's figure, the price before a sale, your starting weight. Use the swap button if you typed them the wrong way round.

Starting from zero or a negative number

A change from zero has no percentage, because any rise from nothing is infinitely large, so the page says so instead of giving a number. When the old value is negative, the page divides by its size without the minus sign, so a move from −50 to −25 counts as a 50% increase. Many textbooks avoid percentage change across zero for this reason; check the convention your course or report uses.

Percentage difference is not the same

Percentage difference compares two numbers when neither is the starting point, such as two shops' prices. It divides the gap by the average of the two: 80 and 100 differ by 20 ÷ 90 = 22.22%. It is shown beside the main answer for that reason.