Formula
Percentage change = (new value - old value) / old value x 100
Variables
- Old value: the baseline or starting value.
- New value: the comparison value after the change.
- Change: new value minus old value.
Positive change example
Revenue rises from 50 to 75. Percentage change = (75 - 50) / 50 x 100 = 50%. The new value is 50% higher than the old value.
Negative change example
A price falls from 80 to 60. Percentage change = (60 - 80) / 80 x 100 = -25%. The negative sign means the new value is lower than the old value.
Percentage change vs percentage points
A rate moving from 10% to 15% increases by 5 percentage points. The relative percentage change is 50%, because 5 is half of the original 10. Mixing those two ideas is a common reporting mistake.
When the formula is not enough
- If the old value is zero, percentage change is undefined because the formula divides by zero.
- Very small baseline values can make a small absolute change look dramatic.
- Negative baselines can be mathematically valid but hard to explain in business or finance contexts.
- Use absolute change beside percentage change when the original size matters.
Common mistakes
- Dividing by the new value instead of the old value.
- Writing a percentage-point difference as a percentage change.
- Comparing percentage changes from different baseline sizes without showing the original values.