Percentage change measures how much a value rose or fell relative to where it started. Subtract the original value from the new value, divide that difference by the absolute original value, and multiply by 100. For a positive baseline, the absolute value is simply the original. Use Percentage Calculator with the percent-change question to keep the starting value and comparison value in the right places.
Choose the baseline before entering numbers
Suppose a club counted 80 attendees at its first event and 100 at its second. The increase is 20 people. Dividing 20 by the original 80 gives 0.25, or a 25% increase. Reversing the events changes the question: falling from 100 to 80 is a 20% decrease. Both statements describe the same pair of counts from different starting points.
Choose % change, then enter the original number in the starting-amount field and the later number in the new-amount field. The field labels change with the selected question. Choose enough decimal places to see a small change, then read the equation below the answer. A positive result indicates an increase when the original value is positive; a negative result indicates a decrease.
Keep the underlying measure consistent. Comparing monthly totals requires the same definition of a month and the same counting method. A percentage calculation cannot repair missing records or make a ten-day total comparable with a thirty-day total.
Percentage points answer a different question
If a completion rate rises from 40% to 50%, it increases by 10 percentage points. Its relative percentage increase is 25%, because 10 divided by 40 is 0.25. Write the unit beside the result so readers know which comparison you mean.
The percent-difference option also answers a different question: it divides the absolute difference by the mean of the two absolute values. It refuses two zeros. That can help compare two measurements without declaring one the starting point, but it should not replace a before-and-after change.
Check awkward starting values
A zero baseline has no ordinary percentage-change result because division by zero is undefined. Report the actual movement, such as from zero signups to twelve signups, instead of inventing an infinite growth percentage. This tool uses the absolute starting value in the denominator for negative baselines too. Moving from -20 to -10 gives a positive 50% change under that convention. Describe the actual amounts beside the percentage, since a relative change around zero can be easy to misread.
For a sale price, Discount Calculator shows the saving and remaining price more directly. For a combined score with unequal contributions, use Weighted Average Calculator rather than averaging percentage changes from unrelated groups. Keep the original counts alongside the percentage when publishing your comparison.