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Percentage Difference Calculator

Compare two values when neither one is the starting point. The percentage difference calculator divides the gap by the average of both numbers, so the answer is the same whichever value you enter first.

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Percentage difference
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How to use the Percentage Difference Calculator

  1. Enter the First value (A) and the Second value (B). Their order does not change the result.
  2. Press Calculate, or keep typing. The percentage difference appears first.
  3. Below it are the absolute difference, the average of the two values, and the percentage change from A to B and from B to A, for when one of them turns out to be the starting point after all.

How it works

percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100

The gap between the two values is divided by their average. The average sits between them, so the result does not depend on which value comes first. A percentage change uses one of the values as its base instead, which is why it gives two different answers for the same pair.

Examples

  • 40 and 60: the gap is 20 and the average is 50, so the difference is 40%.
  • 27.72 trillion and 2.6 trillion: the gap is 25.12, the average is 15.16, and the difference is 165.7%. As a change, the same pair is +966.15% going up and −90.62% going down.
  • $19.99 and $24.99 for the same item at two shops: a difference of 22.23%.

Difference, change, or error?

Use percentage difference when two values stand side by side: two shops' prices, two lab readings, or two countries' figures for the same year. Use percentage change when there is a before and an after, such as last month and this month. Percentage error is a third case, where one value is known to be right and the other is measured against it.

Limitations

  • Both values must be 0 or more. With one negative value the average can be 0 or misleading, so compare the plain gap instead.
  • When both values are 0 there is nothing to express as a percentage.
  • The result can pass 100%. Its ceiling is 200%, reached when one of the values is 0.

Frequently asked questions

How do you calculate the percentage difference between two numbers?

Subtract one from the other and drop the sign, divide by the average of the two numbers, and multiply by 100.

Why does percentage difference give one answer when percentage change gives two?

Change is measured from whichever value is the start. Difference is measured from the average, which is the same for both orders.

Can a percentage difference be more than 100%?

Yes, up to 200%. It happens when two values are far apart, such as 27.72 and 2.6, which differ by 165.7%.

Often used together with Percentage Difference Calculator.