Percentage Change Calculator
Calculate percentage increase or decrease between an original value and a new value.
Enter your values and press Calculate.
Tip: country presets are starting points only. Replace rates and prices with your actual figures whenever possible.
How this calculator works
Percentage change compares the difference between new and original values with the magnitude of the original value.
Formula
A change from 80 to 100 is an increase of 20, equal to 25%.
Getting a more accurate result
- Use the earlier figure as the original value.
- For a decrease, the result will be negative.
- Percentage change is undefined when the original value is zero.
Understanding your result
The result is intended for comparison and planning. Real-world costs can differ because of local taxes, fees, tariffs, financing, usage patterns, equipment efficiency, rounding and other conditions. For important decisions, verify the inputs against your bill, contract, lender, employer or other authoritative source.
Frequently asked questions
Why use the original value in the denominator?
Percentage change measures the difference relative to the starting point.
Is percentage difference the same thing?
No. Percentage difference often compares two values symmetrically using their average.
What happens if the original is zero?
A conventional percentage change cannot be calculated because division by zero is undefined.
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Updated for CostMeter V1.2 • September 2026