What is the difference between percent difference and percent change?

The denominator. Percent change divides by the starting value, so it needs one of the two to be a baseline. Percent difference divides by the mean of both, so it treats them as equals and gives the same answer either way round. From 40 to 60 is a 50% change and a 40% difference.

What is the formula for percent difference?

|a − b| ÷ ((a + b) ÷ 2) × 100. The absolute value on top makes the result positive, and the mean on the bottom makes it symmetric.

Can percent difference exceed 100%?

Yes, up to 200% as one value approaches zero. 1 and 99 have a mean of 50 and a gap of 98, so a percent difference of 196%. It cannot exceed 200% for two positive numbers, which is one of the reasons the measure is used in error analysis.

Which one do labs use?

Percent difference, when comparing duplicate measurements of the same sample, because neither is the truth. When comparing a measurement to a known standard they use percent error instead, which divides by the accepted value — the standard is the baseline.

What about percentage points?

A different thing again. If a rate goes from 40% to 60%, that is 20 percentage points, a 50% increase, and a 40% difference. Newspapers confuse the first two constantly, usually in the direction that makes the number larger.

Percent Difference

With first value 40, second value 60, percent difference comes to 40.00 % — percent difference. It is reached in 6 steps, the last of which is 20 / abs(50) * 100, and each one is printed on the page with its numbers filled in. The formula is the one published by NIST/SEMATECH e-Handbook, not an approximation fitted to it.

Percent difference between two values, divided by their mean — beside percent change, which divides by one of them and gives a different answer.

Formula and sources checked 16 August 2026 · How we check

First value 40, Second value 60

40.00 %

Percent difference for the example below. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.

It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.

First valueSecond value

Percent difference

40.00 %

Absolute difference: abs(40 - 60)20
Mean of the two: (40 + 60) / 250
Percent difference: 20 / abs(50) * 10040 %
Percent change from the first to the second: (60 - 40) / abs(40) * 10050 %
Percent change from the second to the first: (40 - 60) / abs(60) * 100-33.333 %
The second as a share of the first: 60 / 40 * 100150 %

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Worked example

40 and 60 differ by 40%, because 20 over their mean of 50 is 40%. Going from 40 to 60 is a 50% increase, and going from 60 to 40 is a 33.3% decrease. Three answers, all correct, and the one to use depends on whether either value is a baseline.

How to work it out yourself

1.Use percent difference when neither value is the reference — two lab measurements of the same sample, two suppliers quoting the same part, two people’s guesses.
2.Use percent change when one value came first. A price rising from 40 to 60 rose 50%, not 40%, because 40 is the base the increase is measured against.
3.The percent difference is symmetric: swapping the inputs leaves it unchanged. Percent change is not, which is why "40% apart" and "50% more" describe the same pair.
4.Both are undefined when the mean or the base is zero. Two values of +5 and −5 have a mean of zero, and no relative measure exists there.