Change when one value came before the other, difference when they are just two measurements. Reporting a change as a difference is how the same pair of numbers produces two different headlines.

Math & Statisticspercentage

Percentage Difference Calculator

Percentage difference and percentage change, which are different measures constantly used interchangeably. Difference is symmetric; change depends on which value you started from.

Also called: percent difference vs percent change.

Percentage difference

40%

The percentage difference is 40%, computed against the average of the two. Going from 40 to 60 is a 50% change, and going back the other way is -33.33%.

Change from the first to the second

50%

Change from the second to the first

-33.33%

Absolute difference

Average of the two

Ratio

0.67

How this is calculated

Method and background

How this is calculated

Percentage change divides by the starting value, so it is directional: 40 to 60 is a 50% rise while 60 to 40 is a 33.3% fall, from the same pair of numbers. Percentage difference divides by the average instead, which makes it symmetric and gives one answer either way. Use change when there is a before and an after, and difference when comparing two things with no natural order.

difference is symmetric and divides by the average; change is directional and divides by the starting value

a: First value
b: Second value

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

forty against sixty

First value: 40
Second value: 60

Percentage difference40%

The asymmetry this page exists to show

Open this example

identical values differ by nothing

First value: 50
Second value: 50

Percentage difference0%

boundary

Open this example

Method and limits

What it assumes

Both values have the same sign, otherwise the average can approach zero.

What it deliberately does not model

A starting value of zero makes percentage change undefined rather than infinite.
Values of opposite sign make percentage difference unstable and it is not reported.

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Frequently asked questions

Which should I use?: Change when one value came before the other, difference when they are just two measurements. Reporting a change as a difference is how the same pair of numbers produces two different headlines.