About this Percentage Change Calculator
Percentage Change Calculator compares a starting value with a new value and labels the result as an increase or decrease. It is useful for simple before-and-after comparisons where a relative change is more meaningful than the raw difference.
Formula or method
Percentage change = ((new − old) ÷ |old|) × 100.
Example
A change from 80 to 100 is a 25% increase.
Common uses
- Compare prices, counts or measurements over time.
- Measure growth or decline between two reported values.
- Check the percentage impact of an increase or reduction.
How to use this tool
- Enter the values or text requested by the calculator.
- Choose units or options when the tool provides them.
- Select the calculation button and review the result.
- Use the formula, example and notes on this page to check whether the result fits your situation.
Important note
When the starting value is zero, a standard percentage change is undefined.
Frequently asked questions
Why is zero not allowed as the original value?
The standard formula divides by the original value, so starting from zero does not produce a finite percentage change.
Does a negative result mean a decrease?
Yes. The tool reports the magnitude and labels whether the change is an increase or decrease.