Percentage difference compares two positive values relative to their average. It is calculated by dividing the absolute difference between the two values by their average, then multiplying by 100. This metric is used when there is no clear old or new value, providing the relative divergence between two independent measurements or experimental results.

Compare two values and find their percentage difference

Formula

Percentage Difference = (|Value 1 - Value 2| / ((Value 1 + Value 2) / 2)) * 100

How to Calculate Percentage Difference

Enter the two values you want to compare.
Click Calculate to see their percentage difference with steps.

Formula:

Percentage Difference = (|A − B| ÷ ((A + B) ÷ 2)) × 100

What Is Percentage Difference?

Percentage difference shows the relative gap between two values based on their average, not on a single starting point. It’s common in science, data analysis, and economics where you want a fair, symmetric comparison.

Formula

(|A − B| ÷ ((A + B) ÷ 2)) × 100

Need a directional change from an original value instead? Try the Percentage Change Calculator.

Step-by-Step Worked Example

Example: compare 48 and 57.6.

Absolute difference: |57.6 − 48| = 9.6
Average: (57.6 + 48) ÷ 2 = 52.8
Percent difference: 9.6 ÷ 52.8 × 100 = 18.18%

For old→new comparisons instead, see the Percent Increase or Percent Decrease tools.

Excel & Google Sheets Method

You can compute percent difference quickly in a spreadsheet:

Formula: =ABS(B2-A2)/((A2+B2)/2) then format as %.

Safe version: =IF((A2+B2)=0,"",ABS(B2-A2)/((A2+B2)/2))

Common Mistakes to Avoid

Using percentage change when you actually need a symmetric comparison.
Forgetting the absolute value in the numerator.
Dividing by a single value instead of the average of both.
Not handling the zero-average case (result is undefined).

Common Examples

Compare 100 vs 120

Result: 18.18% difference

Compare 80 vs 100

Result: 22.22% difference

Prices: $2.40 vs $2.52

Result: 4.92% difference

Scores: 72 vs 90

Result: 22.22% difference

Negatives: −40 vs −50

Result: 22.22% difference (relative to their average)

Frequently Asked Questions

What is percentage difference?

It measures how much two values differ as a percentage of their average. It’s symmetric, so swapping A and B gives the same result.

How is percentage difference different from percentage change?

Percentage change compares a new value to an original baseline (direction matters). Percentage difference compares two values relative to their average and is not directional.

What’s the formula for percent difference?

Percent Difference = (|A − B| ÷ ((A + B) ÷ 2)) × 100.

Can I use negative numbers?

Yes. The absolute difference handles sign, and the average sets the scale. If the average is 0 (e.g., +x and −x), the result is undefined.

How do I calculate percentage difference in Excel or Sheets?

Use =ABS(A2-B2)/((A2+B2)/2) and format as %. Wrap with IF for safety: =IF((A2+B2)=0, "", ABS(A2-B2)/((A2+B2)/2)).

When should I use percent difference vs percent change?

Use percent difference to compare two independent values (prices at two stores, two measurements). Use percent change to measure movement from a specific starting value.

Key facts

Percentage difference is a symmetric measure used to compare two independent quantities. The average of the two values serves as the reference point, making the calculation order-independent. It is commonly used in laboratory research and quality control to quantify experimental error or variance. Unlike percentage change, this metric does not imply growth or decline, only relative divergence.

Trend & Behavior Analysis

As the absolute difference between the two compared values increases while their sum remains constant, the percentage difference grows linearly. The metric reaches its maximum of 200% when one value is zero and the other is positive. It is highly effective for identifying outliers in datasets where no baseline exists.