Percentage Difference Calculator

How it works

Percentage difference is used when you want to compare two values symmetrically, without designating one as the original and the other as the new value. It is commonly used in science, statistics, and data analysis.

The formula

You find the absolute difference between the two values, divide it by their average, and multiply by 100. The result is always a positive number, regardless of which value is larger.

Why this works: Using the average of both values as the denominator ensures the result is the same whichever order you enter the numbers. If you used just one value as the denominator (as in percentage change), swapping the values would give different answers. The average provides a neutral reference point that makes the comparison perfectly symmetric.

Worked examples

When to use this

Use percentage difference when comparing two values where neither is clearly the "before" or "reference" figure:

• Comparing supplier quotes: Two builders quote £4,200 and £5,600 for the same job. Neither is a reference price; both are current estimates. The 28.57% difference quantifies the spread without implying one is "correct".
• Scientific and lab measurements: Two technicians measuring the same sample get 98 and 102. No single measurement is the reference; you want to know how far apart they are. A 4% percentage difference signals the level of agreement between the two readings.
• Salary benchmarking: Two similar job advertisements pay £32,000 and £38,000. The 17.14% difference helps you understand the range in the market without anchoring to either figure as the norm.
• Regional price comparisons: The same product costs £1.20 in one supermarket and £1.50 in another. Percentage difference gives a neutral measure of the pricing gap across both stores, useful for price comparison reports and consumer journalism.

Understanding the result

Because the average of both values is used as the denominator, the result is always between 0% (identical values) and 200% (one value is zero while the other is positive). Unlike percentage change, which has no upper bound, percentage difference is bounded. The result is always positive regardless of the order you enter the values.

Percentage difference does not indicate direction. It tells you how far apart two values are as a proportion of their midpoint, but it does not say which is larger. If you need to know the direction of change, use the percentage change calculator instead, where you designate a starting and ending value explicitly.

Related concepts

➡ For sequential data where one value clearly comes before the other, the percentage change calculator tracks how one value moved relative to the starting point. ➡ When both values are already percentages and you want the arithmetic gap between two rates, the percentage points calculator finds the raw difference on the same scale. ➡ To express a part-to-whole comparison as a percentage rather than comparing two totals, the ratio to percentage calculator converts any two-part ratio into a percentage of the total.

How to do this in Excel

Put the first value in A1 and the second in B1. ABS ensures the difference is positive regardless of order. The formula divides the absolute difference by the average of both values, then multiplies by 100. You can also use =ABS(A1-B1)/AVERAGE(A1,B1)*100 for a more readable version.

How to do this without a calculator

Find the absolute difference between the two values, ignoring sign. Find the average by adding both values and dividing by 2. Divide the difference by the average and multiply by 100. For £1.20 and £1.50: difference = 0.30, average = 1.35, result = 0.30/1.35 x 100 = 22.2%. For values close together, the average is close to either value, so you can approximate the denominator as roughly the larger value for a quick estimate.

Common mistakes

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