Percentage Change Calculator
Calculate the percentage increase or decrease between an old value and a new value.
About the % Change Calculator
When you have two numbers from different points in time — last year's price versus this year's, or a before-and-after measurement — percentage change tells you how much things moved, expressed as a single signed percentage.
How It Works
The calculator subtracts the old value from the new value to find the raw change, then divides that by the absolute value of the old value and multiplies by 100. A positive result is reported as a percentage increase, and a negative result as a percentage decrease.
Percentage Change (%) = (New Value − Old Value) / |Old Value| × 100.
Example
Scenario: A value moving from 50 to 65.
Result: A percentage increase of 30%.
Assumptions & Limitations
- Uses the absolute value of the old value in the denominator so the sign of the result always correctly reflects an increase or decrease, even if the old value itself was negative.
- If the old value is zero, percentage change is mathematically undefined since you cannot divide by zero — use the raw difference instead in that case.
Frequently Asked Questions
What is the difference between percentage change and percentage difference?
Percentage change is directional and uses the old value as the fixed reference point, while percentage difference (used for comparing two independent values with no clear 'before') divides by the average of the two values instead.
Can percentage change exceed 100%?
Yes — if a value more than doubles, the percentage increase will exceed 100%, which is mathematically correct even though it can feel unintuitive at first.
Why is my result negative?
A negative result means the new value is smaller than the old value, indicating a percentage decrease rather than an increase.