Percent Difference Calculator
This percent difference calculator compares two values when neither is the starting value, such as two measurements or two prices. Example: between 50 and 80 the difference is 46.1538 %.
Example: First value 50 · Second value 80 → Result: Percent difference = 46.1538 % (difference 30, mean 65). Source: Wikipedia – Relative change and difference. Updated: .
How it is calculated
Percent difference compares two numbers without treating either one as the starting value. The reference is the mean of both numbers, so the result is symmetric: it does not change if you swap the values.
Formula and steps
The formula is |a − b| / ((a + b) / 2) · 100. First take the absolute difference, then the mean, divide one by the other and multiply by 100. Unlike percent change, which divides by the starting value, this always gives the same answer whichever number you name first.
Worked example
For 50 and 80 the difference is 30 and the mean is 65. That gives 30 / 65 · 100 ≈ 46.1538 %. For comparison, going from 50 to 80 is an increase of 60 %, going from 80 to 50 a decrease of 37.5 %. Those two figures differ, while the difference relative to the mean does not.
- The result can exceed 100 % but never 200 %: for 0 and 10 it is exactly 200 %.
- If one value is clearly the old one and one the new one, use percent change or a percentage decrease instead.
Frequently asked questions
How do you calculate the percent difference of two numbers?
Divide the absolute difference by the mean of both numbers and multiply by 100. For 50 and 80: 30 / 65 · 100 ≈ 46.1538 %.
How does it differ from percent change?
Percent change divides by the starting value and depends on direction: from 50 to 80 is +60 %, from 80 to 50 is −37.5 %. The percent difference is the same in both directions.
When should I use which formula?
Use percent difference for two equal-standing quantities, such as readings from two devices. For a before-and-after development, percent change fits better.
Sources and legal basis
As of: · Editorial policy
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