CostPercentage 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.
Interpret increases, decreases and negative values
A positive result means the new value is higher; a negative result means it is lower. For positive starting values, this uses the usual (new − old) / old formula. For negative starting values, CostMeter deliberately uses the absolute magnitude of the starting value so moving from −100 to −50 displays +50%. This signed-direction convention is not universal; label it when reporting results.
A zero baseline has no defined percentage change
Moving from 0 to 50 gives an absolute change of 50, but no finite percentage change. Even 0 to 0 has an undefined relative percentage. Report the values and absolute difference instead. An unchanged nonzero baseline gives 0%.
Compare like periods and units
Compare a complete month with another complete month and use the same currency and unit. For rates moving from 4% to 5%, enter 4 and 5: relative change is 25%, while the percentage-point difference is 1. This calculator reports relative change, not percentage points.
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.
Percentage-change examples
If monthly electricity use rises from 800 kWh to 920 kWh, the change is 120 kWh. Dividing 120 by the original 800 gives a 15% increase. If a price falls from $75 to $60, the change is −$15; dividing by the original $75 gives a 20% decrease.
Reversing a percentage change is not symmetrical
A 20% fall followed by a 20% rise does not return to the starting value. A value of 100 falls to 80, then rises to 96 because the second percentage uses 80 as its base. Returning from 80 to 100 requires a 25% increase.
Percentage change versus percentage points
If an interest rate moves from 4% to 5%, it increased by 1 percentage point, but the relative percentage increase is 25%. State which measure you are using so readers do not confuse the two.
Choosing the right comparison
- Use percentage change when one value is clearly the starting point.
- Use percentage difference when comparing two values without a natural baseline.
- Do not enter zero as the original value; the standard calculation would require division by zero.
- Keep the units consistent—for example, compare monthly cost with monthly cost.
Related calculators and guides
Reviewed for CostMeter V1.5 • October 2026