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Compare Two % Values

Use our free Percentage Difference Calculator to measure the difference between two numbers as a percentage. Enter both values to instantly see how far apart they are relative to their average.

How to Calculate Percentage Difference

Percentage difference measures how far apart two values are relative to their average. It is useful when comparing two numbers where neither one is considered the original or starting value.

To calculate percentage difference:

  1. Find the difference between the two values by subtracting the smaller value from the larger value.

  2. Find the average by adding the two values together and dividing by 2.

  3. Divide the difference by the average.

  4. Multiply the result by 100.

 

Formula

Percentage Difference = |Value 1 − Value 2| ÷ ((Value 1 + Value 2) ÷ 2) × 100

The vertical lines around the difference mean that the result is treated as a positive number.

 

Example 1: Comparing Two Prices

Suppose the same item costs £80 from one supplier and £100 from another.

Difference = £100 − £80 = £20
Average = (£80 + £100) ÷ 2 = £90
£20 ÷ £90 × 100 = 22.22%

The percentage difference between the two prices is 22.22%.

 

Example 2: Comparing Test Scores

Two students score 72 and 88.

Difference = 88 − 72 = 16
Average = (72 + 88) ÷ 2 = 80
16 ÷ 80 × 100 = 20%

The two scores have a 20% percentage difference.

 

Example 3: Comparing Measurements

A component measures 50 mm in one test and 56 mm in another.

Difference = 56 − 50 = 6
Average = (50 + 56) ÷ 2 = 53
6 ÷ 53 × 100 = 11.32%

The percentage difference between the measurements is approximately 11.32%.

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When Is Percentage Difference Useful?

Percentage difference is useful when you want to compare two values where neither value is the original or starting point. Unlike percentage increase or decrease, it treats both values equally.

Common uses include comparing prices from different suppliers, test or exam results, measurements from two experiments, sales figures from different locations, production figures, scientific data and other situations where there is no obvious “before” and “after” value.

 

Percentage Difference vs Percentage Change

Percentage difference and percentage change are related calculations, but they answer different questions.

Percentage difference compares two values without treating either one as the starting value. It uses the average of the two values as the basis of the calculation.

Percentage change measures how much a value has risen or fallen from a specific original value. If you have a clear starting value and a new value, percentage change is normally the appropriate calculation.

 

A Common Percentage Difference Mistake

A common mistake is dividing the difference by one of the two values instead of their average.

For example, comparing £80 and £100:

Difference = £20

Dividing £20 by £80 gives 25%, but that treats £80 as the original value and calculates a percentage increase.

For percentage difference, use the average:

Average = £90
£20 ÷ £90 × 100 = 22.22%

 

Frequently Asked Questions

 

Is percentage difference the same as percentage increase?
No. Percentage difference compares two values where neither is considered the original. Percentage increase measures how much a new value has increased from an original value.

 

Can percentage difference be more than 100%?
Yes. If the two values are sufficiently far apart, the percentage difference can exceed 100%.

 

Does it matter which value I enter first?
No. Percentage difference uses the absolute difference between the two numbers, so reversing their order produces the same result.

 

Why does percentage difference use the average?
Using the average gives both values equal importance. This makes the calculation useful when neither number should be treated as the starting value.

 

Should I use percentage difference or percentage change?
Use percentage difference when you are simply comparing two values. Use percentage change when one value is the original and the other is a new value.

 

Related Calculators

Percentage Change Calculator — calculate how much a value has increased or decreased.

Percentage Increase Calculator — calculate how much a value has increased from its original value.

Percentage Decrease Calculator — calculate how much a value has decreased from its original value.

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