Two phrases that sound almost identical, percentage change and percentage difference, actually measure different things, and using the wrong one gives the wrong answer. Understanding percentage change vs percentage difference is worth a few minutes because it comes up constantly: comparing prices, tracking growth, or reporting results. The short version is that percentage change has a clear before and after, while percentage difference simply compares two values with no direction. This guide explains both formulas, works the same numbers through each so you can see how they differ, and shows when to use which. For quick answers on any figures, our percentage calculator does the work.
Quick answer: Percentage change measures how much a value has changed from an original figure: (new minus old) divided by old, times 100. Percentage difference compares two values with no before or after, dividing their difference by their average. From 40 to 50, the change is 25% but the difference is about 22%.
What is percentage change?
Percentage change tells you how much a value has grown or shrunk relative to its original, or starting, value. It has a direction: the result is positive for an increase and negative for a decrease.
Percentage change = ((new value – old value) / old value) x 100
The key point is that you divide by the old value, the starting point. This makes percentage change the right tool whenever there is a clear before and after, such as a price last month versus this month.
What is percentage difference?
Percentage difference compares two values when neither is a natural starting point, so there is no before or after. Because it is symmetric, you divide by the average of the two values, and the result has no direction.
Percentage difference = (|value A – value B| / ((value A + value B) / 2)) x 100
This is the right tool when you are simply comparing two independent measurements, like the readings from two instruments, and it does not matter which comes first.
The same numbers, both ways
Take the values 40 and 50 and run them through each formula.
- Percentage change (40 to 50): (50 – 40) / 40 x 100 = 10 / 40 x 100 = 25%.
- Percentage difference (40 and 50): the average is 45, so 10 / 45 x 100 = about 22.2%.
In plain English: the two answers are different, 25% versus 22%, because they divide by different things. Change divides by the starting value, 40; difference divides by the average, 45. Same numbers, different questions.
Skip the arithmetic
Our percentage calculator handles change and difference for any pair of numbers. For the fundamentals behind these formulas, see our guide on how to calculate percentages.
When to use each
- Use percentage change when one value comes before the other: prices over time, revenue growth, population changes, or any before-and-after comparison.
- Use percentage difference when comparing two values with no natural order: two products, two measurements, or two people’s results.
A simple test: if you can point to a clear original value, use percentage change. If neither value is the obvious starting point, use percentage difference.
Frequently asked questions
What is the difference between percentage change and percentage difference?
Percentage change measures how much a value has changed from an original figure, dividing by that original value, and it has a direction (increase or decrease). Percentage difference compares two values with no before or after, dividing by their average, and has no direction. The same pair of numbers gives different results under each method.
How do I calculate percentage change?
Subtract the old value from the new value, divide by the old value, and multiply by 100. For a change from 40 to 50, that is (50 minus 40) divided by 40, times 100, which equals 25%. A positive result means an increase and a negative result means a decrease. Always divide by the original, starting value.
How do I calculate percentage difference?
Take the absolute difference between the two values, divide by their average, and multiply by 100. For 40 and 50, the difference is 10 and the average is 45, so 10 divided by 45 times 100 is about 22.2%. Because it uses the average, percentage difference is symmetric and has no direction.
Why do percentage change and difference give different answers?
They divide by different reference values. Percentage change divides by the original starting value, while percentage difference divides by the average of the two values. For 40 and 50, change divides by 40 and difference divides by 45, producing 25% and about 22% respectively. Same numbers, but different questions and different denominators.
When should I use percentage difference instead of change?
Use percentage difference when you are comparing two values that have no natural before and after, such as two separate measurements or two products. Use percentage change when one value clearly comes first, like a price last year versus this year. If there is an obvious starting value, change is correct; if not, use difference.
The bottom line
Percentage change measures movement from an original value, dividing by that starting figure, so 40 to 50 is a 25% increase. Percentage difference compares two values with no order, dividing by their average, giving about 22% for the same pair. Use change for before-and-after situations and difference for independent comparisons. For instant results on any numbers, use our percentage calculator.
Further reading
For authoritative background on this topic, see Relative change on Wikipedia.
Note. This article is for general educational purposes. Choose the method that matches your situation, as change and difference answer different questions.
Last reviewed: July 2026