How to calculate percentage difference
- Enter the two values you want to compare in the first card.
- The percentage difference appears instantly, with the calculation shown.
Formula
Percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100. For 40 and 60 the gap is 20 and the average is 50, so the percentage difference is 40%. Swapping the values gives the same answer, because the gap is compared with the average rather than with one of the values.
Difference or change?
Use percentage difference when two values are on an equal footing: two lab measurements of the same quantity, prices in two shops, results from two methods, or two candidates' vote shares. Use percentage change (the second card) when there is a clear before and after, such as last year's and this year's sales. For 40 → 60 the change is +50%, while 60 → 40 is −33.3%; the percentage difference of 40% sits between them.
In science classes you may also see percent error, which compares a measured value with an accepted true value: |measured − true| ÷ true × 100. That is the percentage change card with the true value as the "old" value.
FAQ
What is the difference between percent difference and percent change?
Percent change measures from an old value to a new one; percent difference compares two values symmetrically using their average.
Can percentage difference exceed 100%?
Yes, up to 200% when one value is zero or the values have very different sizes.
How do I calculate percent error?
Use the percentage change card with the true value as the old value and your measurement as the new one, and ignore the sign.