Calculator Problems

How to Calculate Percent Difference Between Two Numbers

Percent difference compares two numbers when neither is the starting point, such as two measurements or two prices. It divides the gap between them by their average, so swapping the values gives the same result.

Last updated: 2 November 2026

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Step-by-step

Enter the two values as A and B.
Read the percent difference shown in the result.
Use the percent change line if one of the values is the original and you want the change from it.
Check the numbers before you report them, since both being zero gives no result.

The formula

Percent difference = |A − B| ÷ ((|A| + |B|) ÷ 2) × 100. For 100 and 120 the gap is 20 and the average is 110, so the percent difference is 18.18%.

Difference versus change

Going from 100 to 120 is a 20% change, because the change is measured from 100. The percent difference is 18.18%, because it is measured against the average. Use the first when there is a starting value, and the second when the two values are equal partners.

Negative values

The calculation uses the size of each number in the average, so a pair such as 5 and −5 gives a clear result of 200%.

USE THE TOOL

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FAQ

Frequently asked questions

What is the percent difference formula?

|A − B| ÷ ((|A| + |B|) ÷ 2) × 100.

Is percent difference the same as percent change?

No. Percent change measures from the first value, while percent difference uses the average of both.

When should I use percent difference?

Use it when neither value is a reference, such as two measurements or two competing prices.

Why is my answer not 20% for 100 and 120?

The tool divides by the average, 110, not by 100. That gives 18.18%.