Percentage change compares an old value to a new value over time: ((new − old) ÷ old) × 100. Percentage difference compares two values with no reference point, using their average as the denominator: (|A − B| ÷ ((A + B) ÷ 2)) × 100.
When to use each
| Question | Use | Denominator |
|---|---|---|
| How much did revenue change since last year? | Percentage change | The old value |
| How far apart are two measured values? | Percentage difference | The average of both |
Example
Compare 100 and 120. Percentage change from 100 to 120 is (20 ÷ 100) × 100 = 20%. Percentage difference is (20 ÷ 110) × 100 ≈ 18.18%, because the denominator is the average (110).
Why it matters
Using the wrong one overstates or understates your result. If there is a clear "before" and "after", use percentage change. If the two values are peers with no order, use percentage difference.
Both start from the same numbers — try Mode 2 and Mode 3 of our percentage calculator.