Percentage Calculator
Use this tool for percent-of-value, increase/decrease percentage, and reverse percentage.
Percent of a value
Result: 36
Percentage change
Change: 25%
Reverse percentage
Original value: 100
Three common percentage problems
Percent of a value answers "what is X% of Y?" (multiply the value by the percent ÷ 100). Percentage change answers "by what percent did this value increase or decrease?" (divide the difference by the original value). Reverse percentage answers "what was the original value before a known percentage change was applied?" (divide the final value by 1 plus the change rate).
Frequently asked questions
Why isn't a 20% increase followed by a 20% decrease back to the original value? Because each percentage applies to a different base amount — the decrease is calculated on the already-increased value, which is larger than the original, so it removes more than the increase added back.
How is percentage change different for a decrease? The formula is the same (new − old) ÷ old × 100 — a decrease simply produces a negative result, which the calculator displays as a negative percentage.
When would I use reverse percentage? It's useful when you know a final price after tax or a discount and need to find the original amount — for example, finding the pre-tax price of an item when you only have the tax-included total and the tax rate.