Percentage Change Calculator
Calculate the percentage increase or decrease between two values.
How to use this tool
Enter the requested information and review the result. Processing occurs in the browser.
Limitations
Results are informational and should be independently verified for important decisions.
Reviewed by: ATOMOS Tools Editorial Team. Last reviewed August 5, 2026.
How percentage change works
Percentage change measures the size of a change relative to the original value. Subtract the original value from the new value, divide that difference by the original value, and multiply by 100. Positive results represent an increase; negative results represent a decrease.
Example calculation
If a monthly cost rises from $80 to $100, the difference is $20. Dividing $20 by the original $80 gives 0.25. Multiplying by 100 gives a 25% increase. If the value falls from $100 to $80, the result is a 20% decrease because the original reference point is different.
Common mistake: reversing the reference value
Percentage increase and percentage decrease are not automatically symmetrical. Always use the original value as the denominator. If the original value is zero, standard percentage-change math is undefined because division by zero is not valid; use an absolute change or another comparison instead.
Interpreting the result responsibly
A percentage change describes relative movement, not whether the underlying amount is large or small. A 50% increase from 2 to 3 is numerically large as a percentage but small in absolute terms. When the context matters, review both the percentage change and the actual difference between the two values.
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