Percentage Difference Calculator
Enter two values to get the percentage difference between them, with every step of the formula, and see how it compares with the percent change from A to B and from B to A.
How to use the Percentage Difference Calculator
- Enter value A and value B. The order does not matter for the percentage difference.
- Choose the number of decimals for the results.
- Press Calculate (results also update as you type).
- Read the steps to see how the absolute difference and the average give the answer.
- Compare with percent change from A to B and B to A, and use the bars to see why they differ.
Percentage difference vs percent change
| Formula | 80 and 100 | Use it when | |
|---|---|---|---|
| Percentage difference | |A − B| ÷ ((A + B) ÷ 2) × 100 | 22.22% | Comparing two values with no "before" and "after" |
| Percent change A → B | (B − A) ÷ |A| × 100 | +25% | A is the old or original value |
| Percent change B → A | (A − B) ÷ |B| × 100 | −20% | B is the old or original value |
All three use the same gap of 20. Only the base changes: 90 (the average), 80 or 100. That is why people quoting "the difference" between two numbers often disagree, and why it helps to say which formula you used.
Worked examples
- Two shop prices, $45 and $52: gap 7, average 48.5, so 7 ÷ 48.5 × 100 = 14.43%.
- Two lab measurements, 9.81 and 9.75: gap 0.06, average 9.78, so 0.06 ÷ 9.78 × 100 = 0.61%.
- Very different values, 10 and 90: gap 80, average 50, so 160%. Percent change from 10 to 90 would be +800%.
Tips
- Percentage difference is symmetric: swapping A and B gives the same answer.
- For positive values it always lies between the two percent changes (ignoring their sign).
- Do not confuse it with a difference in percentage points. Going from 40% to 50% is 10 percentage points, a 25% change, and a 22.22% difference.
- For comparing a measured value with a known true value, use percent error: |measured − true| ÷ |true| × 100.
Frequently asked questions
What is the percentage difference formula?
Percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100. You divide the absolute difference by the average of the two values. For 80 and 100: |80 − 100| = 20, the average is 90, and 20 ÷ 90 × 100 = 22.22%.
What is the difference between percent difference and percent change?
Percent change measures a change from an old value to a new one and divides by the old value, so it has a direction (increase or decrease). Percent difference compares two values with no starting point and divides by their average, so it is the same whichever way round you put them.
Why are the percent changes from A to B and B to A different?
They use different bases. From 80 to 100 is a 25% increase because the gap of 20 is divided by 80. From 100 to 80 is a 20% decrease because the same gap is divided by 100. The percentage difference, 22.22%, sits between them because it uses the average, 90.
When should I use percentage difference?
Use it when neither value is a natural reference point, such as comparing two measurements, two prices from different shops or results from two experiments. If one value is the original or the expected value, use percent change or percent error instead.
Can percentage difference be more than 100%?
Yes, for positive numbers it can go up to 200%. For example, 10 and 90 have a difference of 80 and an average of 50, giving 160%. It reaches 200% only when one value is zero.
What happens with negative numbers or zero?
If the average of the two values is zero, the percentage difference is undefined. With negative numbers this calculator divides by the average of the absolute values and shows a note, because percentage difference is mainly meant for positive quantities.