Percentage Calculator
Calculate any percentage problem: what is X% of Y, what percent is X of Y, or percent change from X to Y.
All three panels update automatically as you type.
Percentages are the most common math people do in daily life and the most common source of mental calculation errors. Tip on a restaurant bill, a 30% off sale, whether a raise was bigger than inflation — all percentages. Having a tool that handles all three directions of the calculation (X% of Y, X as a percent of Y, and percent change) without switching modes covers nearly every practical case.
Quick mental math tricks: To find 15% of a number, find 10% (move decimal left one place) then add half of that. For 20%, just find 10% and double it. For percentage change: subtract, divide by original, multiply by 100.
The three percentage problems
Nearly every percentage question fits one of three forms. What is 15% of 240? Multiply: 240 x 0.15 = 36. 36 is what percent of 240? Divide and multiply: (36/240) x 100 = 15%. What is the percent change from 200 to 240? ((240-200)/200) x 100 = 20% increase. Understanding which form you are solving before calculating prevents the most common errors.
Percentage vs percentage point
If interest rates rise from 4% to 5%, they increased by 1 percentage point, but by 25% as a relative change. If a candidate's poll support rises from 40% to 50%, that is a 10 percentage point increase but a 25% relative increase. The distinction matters in financial and political contexts where "percent increase" is often confused with "percentage point increase."
Frequently asked questions
How do I calculate a tip quickly?
For 20% tip: move the decimal left one place to get 10%, then double it. On a $47 bill: 10% = $4.70, doubled = $9.40. For 15%: find 10% ($4.70) and add half of that ($2.35) = $7.05. The Tip & Bill Split calculator handles this with more options including splitting among multiple people.
How do I work backward from a sale price?
If an item is marked down 30% and costs $84, the original price is $84 / (1 - 0.30) = $84 / 0.70 = $120. A common mistake is adding the discount percent to the sale price, which gives the wrong answer. Always divide by (1 - discount rate) to find the original price.