How to use this tool
Choose the calculation type. For X percent of Y, the formula is X ÷ 100 × Y. For X as a percentage of Y, use X ÷ Y × 100. For change from X to Y, use (Y − X) ÷ X × 100. A zero denominator is rejected. A negative starting value can produce a mathematically valid but unintuitive change; interpret the sign carefully.
Try these values
15% of 200 is 30. 30 as a percentage of 200 is 15%. A change from 80 to 100 is a 25% increase; going back from 100 to 80 is a 20% decrease.
Name the starting number
A percentage is always relative to something. If a price rises from 80 to 100, the increase is compared with 80. If it falls from 100 to 80, the decrease is compared with 100. The absolute change is twenty in both cases, but the percentages differ. Choose the change calculation only when the first number is the original value and the second is the new one.
Do not confuse percent with percentage points
A change from 10% to 15% is an increase of five percentage points. Relative to the original 10%, it is a fifty-percent increase. Both descriptions can be useful, but they answer different questions. Check the wording in a report before putting its numbers into the calculator, and keep enough decimal places if a small rate difference affects a larger total.
Common questions
Why are increase and decrease different?
The starting value is the denominator. Changing the starting value changes the percentage.
Can I use decimals?
Yes. Results are displayed to up to six decimal places; displayed rounding may hide smaller differences.
What happens when the original value is zero?
Percentage change is undefined when the original value is zero, so the tool shows an error.
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