How to use it
Type the two values in any order. Percent difference doesn't depend on the order; the two percent change results do, which is why both directions are shown.
Percent difference vs. percent change
| Percent difference | Percent change | |
|---|---|---|
| Formula | |A − B| ÷ ((A + B) ÷ 2) × 100 | (new − old) ÷ |old| × 100 |
| Reference value | The average of both | The starting (old) value |
| Order matters? | No | Yes |
| Sign | Always positive | + for an increase, − for a decrease |
| Use it for | Two values on an equal footing | A before and an after |
Use percent difference when neither number is the "original": two stores' prices for the same item, two lab measurements of one sample, the populations of two cities.
Use percent change when one value came first: last year's rent vs. this year's, a stock price before and after, a weight at the start and end of a diet. Our percentage calculator covers percent change and the other everyday percentage questions.
Use percent error when one value is the accepted or true value: |measured − accepted| ÷ |accepted| × 100. It's the percent change formula with the accepted value as the reference, without the sign.
Worked example
One store sells a TV for $480 and another for $520.
- Percent difference: |480 − 520| = 40; the average is (480 + 520) ÷ 2 = 500; 40 ÷ 500 × 100 = 8%.
- Percent change from $480 to $520: 40 ÷ 480 × 100 = +8.33% — the pricier store charges 8.33% more.
- Percent change from $520 to $480: −40 ÷ 520 × 100 = −7.69% — the cheaper store charges 7.69% less.
All three are correct; they answer different questions. When you just want to say "the two prices are about 8% apart" without picking a side, percent difference is the neutral choice.
Why the two directions disagree
Percent change divides by the starting value, and the two directions start from different numbers. Going from 10 to 15 is a 50% increase, but going from 15 back to 10 is a 33.33% decrease. Percent difference avoids this by dividing by the midpoint, 12.5, giving 40% either way.
Things to watch
- It can exceed 100%. For positive values percent difference runs from 0% up to 200%, reached when one value is 0.
- Zero and negative values. Percent change from 0 is undefined, and percent difference is only meaningful for positive quantities. With negative numbers this calculator averages absolute values and says so.
- Percentage points. Comparing two rates — 4% and 5% interest — the gap is 1 percentage point. The percent difference is 22.22% and the percent change from 4% to 5% is 25%. Say which one you mean.
- Same units only. Both values must measure the same thing in the same unit.
Frequently asked questions
What is the difference between percent difference and percent change?
Percent difference compares two values against their average and has no direction. Percent change measures how far a new value moved from an old one, so it has a sign and depends on which value came first.
Why is the percent difference between 10 and 15 not 50%?
50% is the percent change from 10 to 15. Percent difference divides the gap of 5 by the average, 12.5, which gives 40%.
Can percent difference be more than 100%?
Yes. For positive values it can reach 200%, which happens when one value is zero. For example, 1 and 9 differ by 8 ÷ 5 × 100 = 160%.
How do I calculate percent error?
Subtract the accepted value from your measured value, take the absolute value, divide by the accepted value and multiply by 100. Measuring 9.6 when the accepted value is 9.8 gives 0.2 ÷ 9.8 × 100 ≈ 2.04%.
Which number should be A?
For percent difference it doesn’t matter. For percent change, make A the earlier or original value and read the "A → B" result.
Last updated: October 8, 2026