Percentage Calculator

How it works

Percentages are one of the most common everyday math operations — tipping, taxes, discounts, exam scores, growth rates. This calculator handles the three most useful percentage operations side by side so you don't need to remember which formula belongs to which problem.

"What is X% of Y" answers questions like "what is 18% of $42.50" — multiply Y by X/100. "X is what percent of Y" answers "I scored 47 out of 60, what percent is that" — divide X by Y, multiply by 100. "Percent change from X to Y" answers "my rent went from $1,500 to $1,650, what's the increase" — subtract, divide by the starting value, multiply by 100.

A few common pitfalls. Percent change uses the *original* value as the denominator, not the new value or the average — going from 100 to 150 is a 50% increase, not 33%. Increases and decreases are not symmetric: a 50% increase reversed is a 33.3% decrease, not a 50% decrease. To increase by X%, multiply by (1 + X/100); to undo it, multiply by 1/(1 + X/100), which is *not* the same as (1 − X/100) for any nonzero X.

Compounding percentages requires care. Two consecutive 10% increases is *not* a 20% increase — it's a 21% increase (1.1 × 1.1 = 1.21). Over many periods this gap grows quickly, which is why financial returns are usually quoted as compound annual growth rates rather than simple averages.

For more elaborate scenarios — discounts plus taxes, repeated discounts, percentage of a percentage — chain the formulas one step at a time and verify intermediate values. Almost every percentage question reduces to one of the three operations on this page.