Percentage Change Calculator
Increase or decrease between two numbers. e.g. “What is the change from 80 to 120?”
Enter your values
Results update as you type. All calculation happens in your browser.
Methodology
Increase or decrease between two numbers. This tool uses a standard, documented formula and runs entirely on your device.
Last reviewed January 2026 · Runs client-side
Reading a percentage change correctly
A percentage change measures how much a value grew or shrank relative to where it started. The starting value is the anchor, the same absolute difference is a bigger percentage when the starting number is small.
The most common error is treating an increase and the decrease that reverses it as the same percentage. They aren't: a 50% rise followed by a 50% fall does not return you to the original number.
How to use this calculator
- Enter the original value.
- Enter the new value.
- Read whether it's an increase or decrease, and by what percentage.
What the inputs mean
- Original value
- The starting point, which the change is measured against.
- New value
- The ending value after the change.
Going from 80 to 120 is a 50% increase. Going back from 120 to 80 is only a 33.3% decrease.
The formula, in plain terms
Change = (New − Original) / Original × 100. A positive result is an increase, a negative one a decrease.
Good to know
- Always divide by the original value, not the new one.
- Increases and their reversing decreases use different percentages because the base changes.
Frequently asked questions
Why isn't a 50% gain cancelled by a 50% loss?
The loss is calculated on the larger, increased value, so it removes more in absolute terms than the gain added.
Last reviewed January 2026. This explainer is general information, not professional advice.