Percentage Calculator
Quickly work out percentages: what is X% of Y, X is what percent of Y, and percent increase or decrease.
Updated 20 Jun 2026 · Free · No sign-up
Percentages come up constantly — tips, discounts, grades, taxes, interest, statistics — and it’s surprisingly easy to muddle them. This percentage calculator handles the three questions you actually run into: what is X% of Y, X is what percent of Y, and the percent change from one number to another. Pick the mode, enter two numbers, and get the answer with the working shown.
The three percentage questions
1. What is X% of Y? Use this for discounts, tips, and shares — e.g. 15% of $200. 2. X is what percent of Y? Use this to turn a part into a percentage — e.g. you scored 42 out of 50, what percent is that? 3. Percent change from X to Y? Use this for increases and decreases — e.g. a price went from $80 to $100, how much did it rise? Each is a different calculation, which is why people mix them up.
The formulas
- X% of Y = (X ÷ 100) × Y
- X is what % of Y = (X ÷ Y) × 100
- Percent change = ((New − Old) ÷ Old) × 100
Worked examples
15% of 200 is (15 ÷ 100) × 200 = 30 — handy for a tip or discount. 42 out of 50 is (42 ÷ 50) × 100 = 84% — a test score. And a price rising from 80 to 100 is ((100 − 80) ÷ 80) × 100 = +25%. Note that a 25% rise followed by a 25% fall does not return you to the start — percentage changes are relative to different bases, a common source of confusion.
Everyday uses
Use mode 1 for sale prices and sales tax, mode 2 for grades and proportions, and mode 3 for tracking changes in prices, salaries, or stats. For tipping at restaurants specifically, our dedicated tip calculator also splits the bill between people. Percentages are everywhere once you start noticing — and getting them right saves real money.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of 200 is (15 ÷ 100) × 200 = 30. Select 'What is X% of Y' in the calculator, enter 15 and 200, and it does this for you and shows the working.
How do I find what percent one number is of another?
Divide the first number by the second and multiply by 100. For instance, 42 out of 50 is (42 ÷ 50) × 100 = 84%. Use the 'X is what % of Y' mode for grades, proportions, or any part-of-a-whole question.
How do I calculate percentage increase or decrease?
Subtract the old value from the new value, divide by the old value, and multiply by 100. A price going from 80 to 100 is ((100 − 80) ÷ 80) × 100 = +25%. A negative result means a decrease. Use the '% change' mode.
Why doesn't a 25% increase then 25% decrease return to the start?
Because each percentage applies to a different base. A 25% rise from $100 gives $125; a 25% fall from $125 (the larger base) is $31.25, landing at $93.75. This asymmetry is a common point of confusion when reading about prices and statistics.