Two ways to compare numbers as percentages. One is directional, one is symmetric. Pick the right one for your context.
Two ways to compare numbers as percentages. Percent change is directional; percentage difference is symmetric. Pick the right one for your situation.
See also: Percentage calculator · How to calculate percentages
| Percent change | Percentage difference | |
|---|---|---|
| Formula | (new − old) ÷ old × 100 | |A − B| ÷ ((A+B)/2) × 100 |
| Symmetric? | No | Yes |
| Direction? | Yes (+ or −) | No (always positive) |
| Use when | Clear baseline / chronology | Comparing equals |
Anytime there’s a clear “before” and “after”, or one value is treated as the baseline:
When neither value is the baseline — typically when comparing two measurements of the same thing or two independent quantities:
Imagine two scientists measure the same plant: one gets 40 cm, the other gets 60 cm. Should the discrepancy depend on whose result is labeled “first”?
Two different numbers for the same discrepancy — unsatisfying. Percentage difference gives a single answer (40%) regardless of order.
Because it always divides by the 'old' value, treating it as the baseline. If A is the baseline, you get one number; if B is, you get another. Percentage difference avoids this by using the average of A and B as the denominator.
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