Percentage Change Calculator
This calculator shows how much a value rose or fell between two readings: last month's price against this month's, revenue in two quarters, weight before and after.
The second mode runs the calculation the other way: it applies a known percentage to a starting value and shows what that value becomes.
Change
+25% increase
Absolute difference: 30 · Ratio: 1.25
Formula: (new − old) ÷ old × 100
The percentage change formula
- Change, % = (new − old) ÷ old × 100.
- From 120 to 150: (150 − 120) ÷ 120 × 100 = +25%.
- From 150 to 120: (120 − 150) ÷ 150 × 100 = −20%.
- The absolute difference is simply new minus old — 30 units in the example above.
Why increases and decreases are not symmetric
Percentages are always measured against the starting value, and that starting value differs for a rise and a fall. A 25% gain followed by a 25% loss does not return to the original figure: 120 → 150 → 112.5.
Undoing a 25% increase takes a 20% decrease. The same rule explains why an asset that drops 50% needs a 100% gain to break even.
Reverse change table
| Increase | Decrease needed to return |
|---|---|
| +10% | −9.1% |
| +20% | −16.7% |
| +25% | −20% |
| +50% | −33.3% |
| +100% | −50% |
| +200% | −66.7% |
Change, difference and ratio
- "Up 100%" and "doubled" describe the same movement.
- A ratio of 1.25 means the new value is 1.25 times the old one, which is a 25% increase.
- A decrease cannot exceed 100%: at that point the value is already zero.
- If the starting value is zero, percentage change is undefined — report the absolute difference instead.
Frequently asked questions
How do I calculate a percentage increase?
Subtract the old value from the new one, divide by the old value and multiply by 100. Going from 120 to 150 is a 25% increase.
How do I calculate a percentage decrease?
Use the same formula; the result comes out negative. Going from 150 to 120 is a 20% decrease.
Why don't a 25% gain and a 25% loss cancel out?
The loss is measured against the higher value. After 120 → 150, a 25% drop lands on 112.5 rather than 120.
What if the starting value is negative?
The calculator divides the difference by the absolute value of the base, so the sign of the result reflects the direction of the change rather than the sign of the base.
How is percentage change different from percentage points?
Percentage points measure the gap between two percentages. A market share moving from 4% to 5% gains one percentage point, which is a 25% increase.
Updated: 2026-08-09