Percentage change turns the difference between two values into a comparison relative to the starting value. That final phrase—relative to the starting value—is the part most often missed.
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Choose the comparison you actually need
For a monthly workload comparison, choose “Percentage change from X to Y,” enter 800 as X and 1000 as Y, and select Get result. The output is 25%. Keep both periods the same length and use the same definition of a visit or completed item. A larger total over a longer period is not necessarily a faster daily rate.
Reversing the comparison changes the base: 1000 down to 800 is a 20% decrease. Do not describe the return trip as a 25% decrease. To compare rates, first calculate each period’s rate on a consistent basis.
Negative starting values need an explanation
This calculator divides by the absolute starting value. From −80 to −60 it reports +25%, because the value rose by 20 relative to a starting magnitude of 80. That can describe a smaller loss, but it is not a universal financial growth convention. From −80 to +20 it reports +125%, crossing zero. State the original and final amounts as well as the convention; readers may reasonably prefer the absolute improvement of 100.
Starting at zero is rejected, including zero to zero. Report the change in units rather than inventing a percentage. Negative values are accepted in the tool; the meaning of the comparison remains your responsibility.
The percentage-change formula
Subtract the original value from the new value, divide by the absolute value of the original, and multiply by 100. A positive answer is an increase; a negative answer is a decrease.
Percentage change = (new value − original value) ÷ |original value| × 100Worked increase example
Suppose monthly visits rise from 800 to 1,000. The difference is 200. Dividing 200 by the original 800 gives 0.25, so the increase is 25%.
(1,000 − 800) ÷ 800 × 100 = 25%Worked decrease example
If a processing time falls from 50 seconds to 40 seconds, the difference is −10. Dividing by the original 50 produces −20%, meaning a 20% decrease.
(40 − 50) ÷ 50 × 100 = −20%Percentage change is not percentage points
A rate moving from 20% to 25% rises by five percentage points. Relative to the original 20%, however, it increased by 25%. State which measurement you mean.
- Percentage points: 25% − 20% = 5 points
- Relative percentage change: (25 − 20) ÷ 20 × 100 = 25%
When the original value is zero
Ordinary percentage change is undefined when the starting value is zero because division by zero has no finite result. Report the absolute change or describe the value as moving from zero instead.