Calculate the percentage increase or decrease between two values.
Instant and private in your browser.
How do you calculate percentage increase or decrease between two values?
Percentage change = (new − old) ÷ |old| × 100. A positive result is an increase; a negative result is a decrease. For example, from 120 to 150 is a 25% increase, while from 150 to 120 is a 20% decrease. Note that an X% increase followed by an X% decrease does not return to the start, because the base value changes.
Understanding your result
Note that an X% increase followed by an X% decrease does not return to the start, because the base value changes.
Formula and method
Percentage change = (new − old) ÷ |old| × 100. A positive result is an increase; a negative result is a decrease.
Assumptions and limitations
It compares two values and reports the change relative to the old one, so the starting value cannot be zero, because dividing by zero is undefined. It measures a single step from old to new, not compound growth across multiple periods or an average rate over time.
Worked example
From 120 to 150 is a 25% increase; from 150 to 120 is a 20% decrease.
How to use this tool
- Enter the original (starting) value.
- Enter the new (ending) value.
- Press Calculate.
About the Percentage Increase / Decrease Calculator
The Percentage Change Calculator shows how much a value has gone up or down in percentage terms — perfect for prices, scores, metrics and growth.
Who should use this tool
Shoppers checking whether a price rise or discount is fair, analysts tracking metric growth, students learning percentage change, and anyone comparing an old value with a new one who wants the increase or decrease stated as a clear percentage.
Benefits
- States any rise or fall as a clear signed percentage
- Measures change relative to the original starting value
- Handles both increases and decreases in one tool
- Runs free in the browser with no account
Practical use cases
- Checking the real size of a shop discount
- Tracking how much a metric grew month on month
- Comparing this year's figure against last year's
- Working out a percentage rise in rent or salary
Frequently asked questions
Why can’t I start from zero?
Percentage change divides by the original value, and dividing by zero is undefined, so the starting value must be non-zero.
Why doesn't a rise then an equal fall return to the start?
Because each percentage is calculated against a different base. Going from 120 to 150 is a 25% increase, but going back from 150 to 120 is only a 20% decrease, since the fall is measured against the larger 150. The base value changes, so the percentages differ.
How do I read a negative percentage change?
A negative result means the value went down. The formula subtracts the old value from the new one, so if the new figure is smaller the result is negative, indicating a decrease. A positive result means the value increased over the same step.