Percentage difference calculator

The percentage difference between 10 and 15 is 40%. Enter two positive numbers to compare their gap with their average, without treating either number as the starting value.

What this calculator does

Percentage difference measures how far apart two values are relative to their shared midpoint. It is useful when comparing two prices, measurements or estimates and neither has priority. Swapping the numbers gives exactly the same percentage, so there is no increase or decrease sign.

Use matching units and compare like with like. Two delivery quotes should cover the same service, and two measurements should use the same scale. The calculator cannot decide whether a difference is important: that depends on your purpose, measurement uncertainty and any agreed tolerance.

Formula

|A − B| ÷ ((A + B) ÷ 2) × 100

Or in one step: 200 × |A − B| ÷ (A + B)

In plain English: subtract one value from the other, ignore the minus sign, divide by their average, then multiply by 100. The vertical bars mean absolute value. Both inputs must be greater than zero. The result is a percentage, not an amount in the original units.

Worked example

Compare 10 and 15. Their absolute difference is 5, and their average is (10 + 15) ÷ 2 = 12.5. Divide 5 by 12.5 to get 0.4, then multiply by 100: the percentage difference is 40%.

Percentage difference versus percentage change

Choose the formula from the question, not from which answer looks smaller. If a price was 80 and is now 100, time gives you a starting point: the percentage change is (100 − 80) ÷ 80 × 100 = 25%. If two suppliers quote 80 and 100 today and neither quote is a reference, percentage difference uses their average of 90 and gives 22.2222%.

Going from 100 back to 80 is a 20% decrease, not a 25% decrease. That happens because percentage change switches its denominator when the direction reverses. Percentage difference remains 22.2222% in either order. If you have an accepted target or true value, a percentage error measured against that reference may be more appropriate than either comparison.

Two more worked examples

Example 2, two lengths: compare 24 cm and 30 cm. The absolute gap is 6 cm. Their average is (24 + 30) ÷ 2 = 27 cm. Divide 6 by 27 and multiply by 100 to get 22.2222%, or 22.22% rounded to two decimal places. The centimetres cancel because both the gap and average have the same unit.

Example 3, two estimates: compare 450 and 550 units. The gap is 100 units and their average is 500 units. The calculation is 100 ÷ 500 × 100 = 20%. Saying that the estimates differ by 20% does not identify which estimate is correct or imply that either estimate changed over time.

Percentage difference in Excel and Google Sheets

Put the first positive value in A1 and the second in B1. Enter =ABS(A1-B1)/AVERAGE(A1,B1) in another cell, then apply percentage formatting. ABS removes the sign of the subtraction, and AVERAGE supplies the shared midpoint. Both Excel and Google Sheets support these functions.

Alternatively, use =ABS(A1-B1)/AVERAGE(A1,B1)*100 and leave the result cell formatted as a number. Do not also apply percentage formatting to this version: that would display a result one hundred times too large. For 10 and 15, the first formula stores 0.4 and displays 40%; the second stores 40. Check that both input cells contain positive numeric values rather than empty cells or text.

Everyday examples

Example	Answer	Try it
Two delivery quotes: 80 and 100	22.2222%
Two lengths: 24 cm and 30 cm	22.2222%
Two estimates: 450 and 550	20%
Two readings: 9.8 and 10.2	4%

Common mistakes

Dividing by the first number instead of the average. That answers a different question and makes the result depend on input order.
Keeping a negative sign after subtracting. Percentage difference describes the size of the gap, so use the absolute difference.
Subtracting two percentages and calling the answer percentage difference. A move from 30% to 40% is 10 percentage points, not a 10% relative difference.
Rounding the average before finishing the calculation. Keep the original numbers and round only the final percentage for your report.

Common questions

What is the percentage difference between 10 and 15?

40%. The gap is 5 and the average is 12.5, so 5 ÷ 12.5 × 100 = 40%. Reversing the inputs to 15 and 10 still gives 40%, because neither value is the baseline.

Is percentage difference the same as percentage change?

No. Difference uses the average of two values. Change uses the starting value and describes direction. Between 10 and 15 the difference is 40%, but a rise from 10 to 15 is a 50% increase.

Can percentage difference be negative?

Not with this formula and two positive inputs. The absolute gap and average are both non-negative, giving a result of zero or more. A negative result normally means you have calculated a signed change instead.

Can I enter zero or negative numbers?

This calculator requires both numbers to be greater than zero. Although some conventions allow one zero, negative values can make the average zero or misleading. Use a method appropriate to your data rather than extending this formula silently.

Can the percentage difference exceed 100%?

Yes. Comparing 10 and 40 gives a gap of 30 and an average of 25, so the difference is 120%. For two strictly positive numbers the result is always below 200%, even when one value is much larger.

What if the two numbers are identical?

The percentage difference is 0%. For example, 25 and 25 have a gap of zero and an average of 25. Zero divided by that positive average is zero. This is a valid comparison, unlike entering two zeros.

How many decimal places should I report?

That depends on the precision of your inputs and reporting rules. The calculator displays up to four decimal places for percentages. Two decimal places are often sufficient for a written comparison, but keep extra digits while doing further calculations.

Last reviewed 8 November 2026. Results use exact decimal arithmetic and are rounded once for display.