Everyday maths
How to calculate percentage change
Percentage change measures the difference relative to the starting value. The original value belongs in the denominator because it is the baseline.
Open the percentage change calculatorPercentage change = (new − original) ÷ |original| × 100
Calculate an increase
Monthly orders rise from 240 to 300.
- Find the change: 300 − 240 = 60.
- Divide by the original: 60 ÷ 240 = 0.25.
- Multiply by 100: 25% increase.
Calculate a decrease
A price falls from $80 to $68. The signed change is $68 − $80 = −$12. Then −12 ÷ 80 × 100 = −15%, meaning a 15% decrease.
| Original | New | Percentage change |
|---|---|---|
| 50 | 65 | 30% increase |
| 50 | 35 | 30% decrease |
| 120 | 120 | 0% |
Why reversing the values changes the answer
Moving from 80 to 100 is a 25% increase because 20 is 25% of 80. Moving back from 100 to 80 is a 20% decrease because 20 is 20% of 100. Percentage change is directional.
This also explains why a 50% loss needs a 100% gain to return to the starting value. Falling from 100 to 50 loses 50; gaining 50 from the new base of 50 is 100%.
Zero and negative starting values
Percentage change from zero is undefined because division by zero is impossible. Report the absolute change instead, or explain that the quantity rose from zero.
Changes involving negative baselines can be mathematically calculated using an absolute original denominator, but the interpretation depends heavily on context. For profit moving from a loss to a gain, absolute amounts often communicate more clearly than a percentage.
Check the change online
The free Percentage Change Calculator shows the signed difference and whether the result is an increase or decrease. Enter the earlier value as original and the later value as new.