Percent Difference Calculator
Compare two values when neither one is the starting point.
Difference = |50 − 65| = 15Average = (50 + 65) ÷ 2 = 57.515 ÷ 57.5 × 100 = 26.087%
How to calculate percent difference
- Find the absolute difference between the two values: |A − B|.
- Find their average: (A + B) ÷ 2.
- Divide the difference by the average and multiply by 100.
For 50 and 65: the difference is 15, the average is 57.5, and 15 ÷ 57.5 × 100 = 26.087%.
Percent difference vs. percent change
| Percent change | Percent difference | |
|---|---|---|
| Question it answers | How much did it go up or down? | How far apart are these two values? |
| Divides by | The old value | The average of both values |
| Has a direction (+/−) | Yes | No, always positive |
| 50 and 65 | +30% (50 → 65), −23.077% (65 → 50) | 26.087% either way |
If one value clearly came first, use the percent change calculator. If you are comparing a measurement against a known correct value, use percent error instead.
A note on negative values
The textbook formula is meant for positive quantities. With negative inputs, (A + B) ÷ 2 can be zero or negative, which makes the result meaningless. This calculator uses the average of the absolute values as the denominator, which gives the textbook answer for positive numbers and a sensible one otherwise.
Frequently asked questions
What is the percent difference formula?
Percent difference = |A − B| ÷ ((A + B) ÷ 2) × 100. It divides the gap between two values by their average.
What is the difference between percent difference and percent change?
Percent change measures a change from an old value to a new value and divides by the old value. Percent difference compares two values with no starting point and divides by their average, so the answer is the same whichever value you put first.
Does the order of the numbers matter?
No. The percent difference between 50 and 65 is 26.087%, and so is the percent difference between 65 and 50.
When should I use percent difference?
When neither value is a baseline, for example comparing prices at two shops, results from two labs, or two measurements of the same thing.