Math guide
Percentage Difference vs. Percentage Change
These two measures are constantly confused, and using the wrong one can make the same two numbers look 33% apart or 40% apart. The difference is what you divide by.
Last reviewed 2026-08-01
Percentage change: movement over time
Use change when there is a clear before and after: prices, population, speed.
Change = (New − Old) ÷ Old × 100. It has a direction (up or down) and a base (the old value).
Percentage difference: two values, no direction
Use difference when neither value is 'the original' — comparing the heights of two people, or two competing prices for the same item.
Difference = |A − B| ÷ average(A, B) × 100. It is always positive and symmetric: A vs B gives the same answer as B vs A.
The same numbers, both ways
Store A sells an item for $80, store B for $100.
As a change from A to B: (100 − 80) ÷ 80 = +25%. As a symmetric difference: 20 ÷ 90 ≈ 22.2%.
Both are correct — they answer different questions. Trouble starts when a '25% difference' claim was actually computed as a change, or vice versa.
How to choose
- Is one value earlier or original? → percentage change.
- Are you comparing two peers with no baseline? → percentage difference.
- Reading someone else's figure? → check what they divided by before trusting it.
Put it into practice
- Percentage CalculatorFind what a percentage of a number is, what percent one number is of another, and the percentage change between two values.
- Percentage Increase CalculatorCalculate the percentage increase from a starting value to a new value, or apply an increase directly.
- Average CalculatorCalculate the arithmetic mean of a set of numbers, along with the count, sum, minimum, and maximum.