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Percentage Difference Calculator

Use this free online percentage difference calculator to compare two values when neither is the clear baseline. It uses the average of both values as the reference point.

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Formula

Percentage Difference = (|A - B| / ((A + B) / 2)) × 100

Take the absolute difference of the two values, divide by their average, and multiply by 100.

Worked Example

Value A: 40, Value B: 60 Step 1: Absolute difference → |40 - 60| = 20 Step 2: Average → (40 + 60) / 2 = 50 Step 3: Divide → 20 / 50 = 0.4 Step 4: Multiply by 100 → 40% Result: 40% difference.

What Is Percentage Difference?

Percentage difference measures the relative gap between two values when neither is the clear "original" or "baseline." Unlike percentage change (which compares to a starting value), percentage difference uses the average of both values as the reference point, making it symmetric.
  • Comparing test scores of 80 and 90 gives a percentage difference of about 11.8%
  • The result is always positive because it uses the absolute value of the difference
  • The maximum possible percentage difference is 200% (when one value is 0)
  • Order does not matter: comparing A to B gives the same result as B to A

Percentage difference is ideal for comparing measurements, survey results, experimental data, and any two quantities where neither serves as the clear reference point.

You can also calculate changes using our Percentage Calculator, Percentage Increase Calculator or Percentage Decrease Calculator.

Frequently Asked Questions

When should I use percentage difference vs percentage change?

Use percentage difference when neither value is clearly the "original" (e.g., comparing two cities). Use percentage change (increase or decrease) when comparing to a baseline value over time.

Can percentage difference exceed 200%?

No. The theoretical maximum is 200%, which occurs when one value is 0 and the other is non-zero. In practice, most real-world comparisons produce much smaller values.

Is percentage difference always positive?

Yes, because it uses the absolute value of the difference. The order of the two values does not affect the result.

Why use the average as the base instead of one of the values?

Using the average treats both values equally, which is fair when neither is the "original." If you used one value as the base, swapping A and B would give a different result, which can be misleading.

How is percentage difference used in science?

Scientists use it to compare experimental results with expected values, compare measurements from different instruments, or quantify how much two datasets differ without assigning one as the "correct" value.

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