Home / Percentage Calculator
Percentage Calculator
Six of the percentage calculations people actually need, side by side on one page.
The percentage formulas behind each calculator
"X% of Y" is Y × (X/100). "What percent is X of Y" is (X/Y) × 100. Percentage change from X to Y is ((Y−X)/|X|) × 100 — positive for an increase, negative for a decrease. To increase or decrease a number X by Y%, multiply by (1 ± Y/100). And for the reverse question — "X is Y% of what number?" — divide X by (Y/100).
A worked example
Suppose a $200 item is marked down and you're told the sale price is $170. The percentage change is ((170−200)/200) × 100 = −15%, a 15% decrease. If instead you knew the discount was 15% and wanted the original price from a $170 sale price, you'd compute the reverse: since sale price = original × (1 − 0.15), the original is 170 / 0.85 ≈ $200.
Frequently asked questions
How do I calculate "X percent of Y"?
Multiply Y by X ÷ 100. For example, 15% of 200 is 200 × (15/100) = 30.
How do I find what percent one number is of another?
Divide the first number by the second, then multiply by 100: (X ÷ Y) × 100. For example, 30 is 15% of 200.
What's the difference between percentage change and percentage points?
Percentage change measures the relative change between two values as a percentage of the starting value: ((new − old) / |old|) × 100. Percentage points measure the raw arithmetic difference between two percentages, without dividing by the starting value.
How does the reverse percentage calculation work?
If X is Y% of some number, that number equals X ÷ (Y/100). For example, if 30 is 15% of a number, that number is 30 ÷ 0.15 = 200.