How to Calculate Percentage Increase and Decrease
Calculate percentage change correctly and understand why reversing a change produces a different percentage.
A value rises from 80 to 92
Formula: (92 − 80) ÷ 80 × 100 = 15%.
Increase formula
Subtract the original value from the new value. Divide that increase by the original value, then multiply by 100. Keeping the original value in the denominator is the key step.
- New value − original value = change.
- Change ÷ original value = decimal change.
- Decimal change × 100 = percentage increase.
Decrease formula
For a decrease, subtract the new value from the original value, divide by the original, and multiply by 100. A drop from 92 to 80 is 12 ÷ 92, or about 13.04%.
- The 15% increase from 80 to 92 is not reversed by a 15% decrease.
- The base changes from 80 to 92, so the reverse percentage changes too.
- Always identify which value is the starting point.
Common uses
Percentage change helps compare price adjustments, revenue growth, discounts, test scores, and measurements of different sizes. When the original value is zero, ordinary percentage change is undefined because division by zero is not possible.
Frequently asked questions
Why are percentage increase and decrease not symmetrical?
They use different starting values. The denominator changes when the direction changes.
What if the original number is negative?
The formula can produce a result, but interpretation depends on context. Explain the underlying values alongside the percentage.