Percent Change Calculator

Increase or decrease measured against a starting value.

The formula

The result is signed. A positive answer is an increase, a negative one a decrease. Dividing by the original is what makes this a change rather than a difference: the starting value is the reference point.

Worked example

A price rises from $50 to $75. The difference is $25, and 25 ÷ 50 = 0.5, so the change is +50%. Running it backwards, $75 down to $50 is a difference of −25 over 75, which is −33.3%.

Why the two directions differ

This surprises people, and it is not an error. Going up divides by 50; coming back down divides by 75. A 50% rise is undone by a 33.3% fall, not another 50%. Any claim that a value 'fell 50% then rose 50%, so it is back to even' is wrong — it is 25% down.

When the original is zero

Percent change is undefined. There is nothing to measure against, and the calculator will say so rather than return infinity.

Percentage points are different again

If a rate goes from 4% to 6% that is a rise of 2 percentage points, but a 50% percent change. News reports mix these constantly. State which you mean.