This percentage calculator answers the three most common percentage questions: What is X% of Y?, X is what percent of Y?, and What is the percentage change from X to Y? Type in any box and the answer appears instantly, along with the working.
1. What is X% of Y?
2. X is what percent of Y?
3. Percentage change from X to Y
Percentage Formulas
“Percent” means “per hundred”, so 25% is 25 out of 100, or 0.25. Every percentage problem uses the same relationship: part = percent ÷ 100 × whole. Rearranging it gives the three formulas the calculator uses.
1. Percent of a number
Result = Percent ÷ 100 × Number
Example: 20% of 150 = 20 ÷ 100 × 150 = 30.
2. What percent one number is of another
Percent = Part ÷ Whole × 100
Example: 30 is what percent of 150? 30 ÷ 150 × 100 = 20%. This is how you turn a test score of 42 out of 50 into a percentage: 42 ÷ 50 × 100 = 84%.
3. Percentage change (increase or decrease)
Change % = (New − Old) ÷ Old × 100
Example: a price goes from $80 to $100. (100 − 80) ÷ 80 × 100 = 25% increase. If it goes back from $100 to $80, that is (80 − 100) ÷ 100 × 100 = 20% decrease.
A rise and a fall of the same amount are not the same percentage, because each is measured from a different starting value. A 25% increase followed by a 20% decrease brings you back to where you started.
Quick Mental Math
- 10%: move the decimal point one place left. 10% of 340 = 34.
- 5%: half of 10%. 5% of 340 = 17.
- 1%: move the decimal point two places left. 1% of 340 = 3.4.
- Swap trick: X% of Y is the same as Y% of X. 8% of 50 = 50% of 8 = 4.
Common Uses
- Discounts: 30% off $60 is 30% of 60 = $18 off, so you pay $42. See the Discount Calculator.
- Tips: 18% of a $45 bill is $8.10. See the Tip Calculator.
- Grades: 27 out of 30 is 90%.
- Salary raises and price changes: use the percentage change formula.
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.
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100. For example, 45 out of 60 is 45 ÷ 60 × 100 = 75%.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100. From 50 to 65 is (65 − 50) ÷ 50 × 100 = 30% increase.
What is the difference between percentage change and percentage points?
If an interest rate goes from 4% to 5%, it rose by 1 percentage point, but by 25% in relative terms, because (5 − 4) ÷ 4 × 100 = 25%.