They sound interchangeable, but percentage difference and percentage change answer different questions — and using the wrong one can change your answer by several points. Percentage change measures how much a value has moved from an original value to a new one, so it has a direction. Percentage difference measures how far apart two values are when neither is the original, so it has no direction and is always positive.
Here is the classic illustration. Take the numbers 80 and 100:
- 80 → 100 is a +25% change
- 100 → 80 is a −20% change
- The percentage difference between 80 and 100 is 22.2% — whichever order you put them in
Three different answers from the same two numbers. This guide explains both formulas, when to use each, and how to avoid the mistakes that trip most people up. If you just want the answer for your own numbers, our Percentage Calculator handles both.
The one-sentence difference
Percentage change compares a new value to an original value: it answers “how much did this grow or shrink?”
Percentage difference compares two values to each other, using their average as the reference: it answers “how different are these two things?”
The reference point is everything. Change has a built-in baseline (the original), difference deliberately has no baseline, so it uses the midpoint between the two values instead.
Percentage change: formula and examples
Percentage change = ((New value − Original value) ÷ Original value) × 100
A positive result is an increase; a negative result is a decrease.
Example 1 — a pay rise. Your salary goes from £50,000 to £55,000: (55,000 − 50,000) ÷ 50,000 × 100 = +10% change
Example 2 — a price drop. A jacket falls from £120 to £90: (90 − 120) ÷ 120 × 100 = −25% change
Notice that the denominator is always the original value. That is why going from 80 to 100 is +25% but coming back from 100 to 80 is only −20%: the same absolute move is a different share of a different base.
Percentage difference: formula and examples
Percentage difference = (|Value A − Value B| ÷ Average of A and B) × 100
The vertical bars mean absolute value — the result is never negative. The denominator is the midpoint between the two values.
Example — two scales, one parcel. One scale weighs a parcel at 4.8 kg, another at 5.2 kg. Neither reading is “the original” — you just want to know how far apart they are: |5.2 − 4.8| ÷ ((5.2 + 4.8) ÷ 2) × 100 = 0.4 ÷ 5.0 × 100 = 8.0% difference
Percentage difference is the standard tool in science and engineering for comparing two measurements where neither is privileged. LibreTexts’ guide to calculating percent change and difference draws exactly this line: use percent change for before/after within the same subject, and percent difference for comparing two independent measurements.
Same numbers, both formulas
The fastest way to feel the distinction is to run one pair of numbers through both:
| Calculation | Working | Result |
|---|---|---|
| Change from 80 to 100 | (100 − 80) ÷ 80 × 100 | +25% |
| Change from 100 to 80 | (80 − 100) ÷ 100 × 100 | −20% |
| Difference between 80 and 100 | 20 ÷ 90 × 100 | 22.2% |
Change flips sign and size depending on direction; difference sits between the two and never changes with order.
Side-by-side comparison
| Percentage change | Percentage difference | |
|---|---|---|
| Question it answers | How much did it grow or shrink? | How far apart are these two values? |
| Reference point | The original value | The average of the two values |
| Direction | Yes — positive or negative | No — always positive |
| Order matters? | Yes | No (symmetric) |
| Formula | (New − Original) ÷ Original × 100 | |A − B| ÷ ((A + B) ÷ 2) × 100 |
| Typical uses | Prices over time, salary rises, growth rates, discounts | Comparing measurements, methods, products or quotes |
When to use which
Use percentage change when there is a genuine “before”:
- A price, wage, rent or metric at two points in time
- Before-and-after results of the same thing (a test score after studying, revenue after a campaign)
- Discounts and markups, where the original price is the reference
Use percentage difference when there is no natural baseline:
- Two instruments or methods measuring the same thing
- Two quotes, estimates or forecasts for the same job
- Experimental vs. theoretical values in a lab report
- Two similar products’ specs, where neither is the “original”
A simple test: if you can point at one value and say “that’s the starting point,” use change. If both values are on equal footing, use difference.
The related trap: percentage points
One more distinction that news headlines routinely blur. If an interest rate rises from 4% to 5%, that is 1 percentage point — but it is a 25% percentage change ((5 − 4) ÷ 4 × 100). Both statements are true; they measure different things. “Percentage point” is the absolute difference between two percentages, while “percentage change” is the relative change.
Common mistakes to avoid
- Using percentage difference when a baseline clearly exists. If a price rose from £80 to £100, “25% increase” is the meaningful statement; “22.2% difference” hides the direction.
- Dividing by the new value in a change calculation. The denominator is always the original value. Dividing by the new one is how a +25% rise gets misreported as 20%.
- Expecting difference to show direction. By design it cannot — if it matters which value is bigger, say so in words alongside it.
- Averaging incorrectly. The difference denominator is the average of the two values, not the larger or smaller one.
Reverse percentages are close cousins of this topic — working out the price before VAT or before a discount uses the same “divide by the original relationship” logic, which is why our VAT Calculator and the guide to removing VAT from a price trip up on exactly the same mistake: applying a percentage to the gross price instead of the net price.
Work it out instantly
If you would rather not keep two formulas in your head, the Percentage Calculator computes percentage change and percentage difference from your two numbers — enter them, pick the calculation you need, and it does the rest.
Frequently asked questions
Is percentage difference the same as percentage change?
No. Percentage change measures movement from an original value to a new value and can be positive or negative. Percentage difference measures the gap between two values, using their average as the reference, and is always positive.
Why is percentage difference always positive?
Because its formula uses the absolute difference between the two values and divides by their average. It measures the size of a gap, not its direction — the same reason it gives the same answer regardless of which value you list first.
Which should I use to compare two prices?
It depends on the relationship. If one price is the original (for example, last month’s price) and the other is the new price, use percentage change. If you are comparing two current prices side by side, with neither as the original, use percentage difference.
Can percentage change be more than 100%?
Yes, for increases — a value that grows from 40 to 100 has increased by 150%. Decreases of positive values cannot exceed 100%, because that would take the value below zero.
