Percent Change Calculator

Measure increase or decrease between two values as a percentage.

How to use this tool

Enter the old and new values.
Choose percent change, difference, or both.
Read the result with the sign label.

How it works

Change = (new - old) / |old| x 100. Difference = |a - b| / ((a + b)/2) x 100.

Tips

Percent change is directional; use percentage difference to compare two values fairly.
When old is near zero, percent change is extreme — quote absolute numbers.

Limitations

Percent change with an old value of zero is undefined; the tool guards against it.

Frequently asked questions

How is percent change computed?

(New - Old) / |Old| x 100. If something goes from 40 to 50, that's a 25% increase.

What is 'percentage difference'?

The absolute difference between two values as a percentage of their average — symmetric, so which is 'first' doesn't matter.

Can the change be negative?

Yes — a 'decrease' returns a negative number, or choose display that labels it a decrease.