About the Percentage Change Calculator
Calculate the increase or decrease between two numbers relative to the original value.
Formula or method
Difference = new value − original value. Percentage change = difference ÷ absolute original value × 100 under this tool's convention.
Worked example
From 100 to 120 is a 20% increase. From 120 back to 100 is about a 16.67% decrease because the starting base differs.
How to use the tool
Start with the example values above, then replace each input with your own figures. The results update immediately. Review the units, denominators, and assumptions before using any number in an important decision.
Assumptions and limitations
Percentage change from zero is undefined. This calculator divides by the absolute original value for negative starting values; other disciplines may use different conventions.
Frequently asked questions
Why don't a 20% rise and 20% fall cancel?
Because each percentage uses a different starting value. For example, 100 increases to 120 and then falls to 96 after a 20% decline.
Privacy and support
Your inputs are processed locally in your browser. ToolMosaic does not upload or store the values you enter in this tool. Our tools are free, and we appreciate your support.