How it works
Percentage of a value multiplies the value by the percentage and divides by 100.
What-percentage divides the part by the whole and multiplies by 100.
Percentage change compares the difference between two values to the original value, so it is positive for an increase and negative for a decrease.
Reverse percentage works backwards from a value that has already been increased or decreased by a percentage, to find what it started as.
Formula: Percentage of a value: value × percentage ÷ 100. Percentage change: (new − original) ÷ original × 100.
Examples
Percentage of a value
20% of 150 is (20 ÷ 100) × 150 = 30.
What percentage
30 is (30 ÷ 150) × 100 = 20% of 150.
Percentage change
A price moving from 80 to 100 is a change of ((100 − 80) ÷ 80) × 100 = 25%.
Reverse percentage
A value of 120 after a 20% increase started at 120 ÷ 1.20 = 100.
Things to keep in mind
- Percentage change and percentage difference are not the same calculation: change is directional and uses the original value as its base, while difference treats two values symmetrically. This page covers percentage change; see the Percentage Difference Calculator (planned) for the symmetric version.
- A percentage change cannot be calculated from an original value of zero, since there is nothing to compare the change to — the calculator explains this rather than showing an error code.
- Reversing a 100% decrease is undefined, since a 100% decrease always gives zero regardless of the starting value.