Percentage Difference Calculator

About this tool

The Percentage Difference Calculator compares two numbers when neither one is the obvious starting point. Enter values A and B and it returns the percent difference, |A − B| ÷ ((A + B) ÷ 2) × 100, along with the percent change from A to B and from B to A, each worked out with your numbers. For 10 and 15, the percent difference is 40%, while the change is +50% going up from 10 and −33.3333% going down from 15. That gap is why the choice of formula matters: percent difference divides by the average, so it gives the same answer whichever value comes first, while percent change divides by the original value. A swap button flips A and B. Zero and negative values get plain explanations: percent change from 0 cannot be calculated, and with negative inputs the average uses absolute values. Results show up to four decimal places. The calculator runs in your browser.

Why use it

• Shows the percent difference and the percent change in both directions at once, so you can see how much the choice of formula matters.

• Writes out every formula with your numbers, which is handy for lab reports and homework.

• Explains zero and negative values instead of showing errors or misleading numbers.

• Labels each percent change as an increase or a decrease.

• Updates instantly as you type, right in your browser.

How to use

1. Enter the first value as A and the second as B; the order does not affect the percent difference.
2. Read the percent difference in the first card.
3. If one value is a before or original figure, read the percent change cards for A to B and B to A.
4. Review the worked formulas to see each step with your numbers.
5. Press Swap A and B to flip the direction of the percent change.

When it helps

• Comparing two measurements of the same thing, such as two lab trials or two instrument readings.
• Comparing the price of the same product at two stores.
• Checking how far apart two survey results or test scores are when neither is the baseline.
• Reporting a before-and-after change, using the percent change cards.

Examples

Tips

• If one value is an accepted or true value, you want percent error, |measured − true| ÷ |true| × 100, rather than percent difference.
• For two positive values, the percent difference can never exceed 200%, because the gap can never be more than twice their average.
• When comparing two percentages, such as 40% and 45%, the gap is 5 percentage points, while their percent difference is 11.7647%.
• Percent change is not symmetric: a rise from 10 to 15 is +50%, but the fall back from 15 to 10 is −33.3333%.

Frequently Asked Questions

Glossary

Percent difference

The absolute gap between two values as a percentage of their average.

Percent change

The change from an original value to a new value as a percentage of the original.

Absolute value

A number's distance from zero, written |x|; |−5| = 5.

Percentage point

The simple difference between two percentages; going from 40% to 45% is a rise of 5 points.

Reference value

The value treated as the starting point or baseline in a percent change.