To find the percentage difference between two numbers, enter them as Value A and Value B. The calculator divides the gap between them by their average and multiplies by 100, then shows each step. It also lists the percentage change from A to B and the absolute difference, and Swap values flips the order.
How to use the percentage difference calculator
- Enter Value A. Type the first number, for example the price at one shop or your first measurement.
- Enter Value B. Type the second number. The order doesn't change the percentage difference, only the percentage change.
- Read the results. The percentage difference appears with its working steps. Below it you'll see the percentage change from A to B and the absolute difference.
- Swap if needed. Select Swap values to see the percentage change in the other direction. The percentage difference stays the same.
Percentage difference formula
The percentage difference compares the gap between two values with their average:
Percentage difference = |A - B| ÷ ((A + B) ÷ 2) × 100
The vertical bars mean "absolute value", so the gap is always positive. Using the average as the reference point treats both numbers equally, which is why swapping A and B gives the same answer.
For two non-negative numbers (not both zero) the result falls between 0% and 200%. It reaches 200% only when one of the values is zero.
How to calculate percentage difference, step by step
Example: one lab measures a sample at 40 g and another at 50 g.
- Find the absolute difference: |40 - 50| = 10.
- Find the average: (40 + 50) ÷ 2 = 45.
- Divide the difference by the average: 10 ÷ 45 = 0.2222.
- Multiply by 100: 0.2222 × 100 = 22.22%.
Another example with prices: a book costs 12.50 in one shop and 14.00 in another. The gap is 1.50, the average is 13.25, and 1.50 ÷ 13.25 × 100 = 11.32%.
Percentage difference vs percentage change
The calculator shows both numbers because people often mix them up. They answer different questions.
| Percentage difference | Percentage change | |
|---|---|---|
| Formula | |A - B| ÷ average × 100 | (B - A) ÷ |A| × 100 |
| Compared with | The average of both | The starting value A |
| Order matters | No | Yes |
| Sign | Always positive | Positive or negative |
| 40 and 50 | 22.22% | +25% (A to B), -20% (B to A) |
Use percentage difference when neither value is the original: two shops' prices, two people's scores, two instruments measuring the same thing. Use percentage change when one value came first and the other is what it became: last year's salary and this year's, a price before and after a sale. For change, discounts and "X% of Y" sums, the percentage calculator has a mode for each.
Common mistakes with percent difference
- Dividing by one of the values. 10 ÷ 40 gives 25% and 10 ÷ 50 gives 20%. Neither is the percentage difference; those are percentage changes in each direction.
- Confusing percent with percentage points. If one survey shows 40% and another 50%, the gap is 10 percentage points. The percentage difference between them is 22.22%.
- Using it as percent error. In a science lab, percent error compares your result with a known accepted value: |measured - accepted| ÷ accepted × 100. Percentage difference is for two measurements when neither is known to be correct.
- Comparing different units. 2 feet and 50 cm can't be compared until both are in the same unit. Convert one first with the unit converter.
- Mixing signs. The formula assumes both values are positive. If A + B is zero, the average is zero and there's no answer.
Frequently asked questions
What is the percentage difference formula?
Percentage difference = |A - B| ÷ ((A + B) ÷ 2) × 100. You divide the absolute gap between the two values by their average, then multiply by 100.
How do I calculate the percentage difference between two numbers?
Subtract one number from the other and ignore the sign, divide by the average of the two numbers, and multiply by 100. For 40 and 50: 10 ÷ 45 × 100 = 22.22%.
What's the difference between percentage difference and percentage change?
Percentage change measures movement from an old value to a new one and divides by the old value, so direction matters. Percentage difference compares two values on equal terms by dividing by their average, so the order doesn't matter.
Why does swapping the values change the percentage change but not the difference?
Percentage change divides by the starting value, which changes when you swap. Percentage difference divides by the average, which stays the same whichever value comes first.
Can the percentage difference be more than 100%?
Yes. For two non-negative numbers it can go up to 200%, which happens when one value is zero. For example, 10 and 50 have a gap of 40 and an average of 30, so the percentage difference is 133.33%.
Is a percent difference calculator the same as a percent error calculator?
No. Percent error divides by a known accepted value. Percent difference divides by the average of two values when neither one is the reference.