Percentage Calculator: X% of Y, Percent Change and More
This free percentage calculator answers the five percentage questions people ask most: what is X% of a number, what percent one number is of another, the percentage change between two numbers, a number increased or decreased by a percent, and the original number before a percentage was taken. Type in any box and the answer updates instantly.
1. Percent of a number
2. What percent is it?
3. Percentage change
4. Increase or decrease by a percent
5. Reverse percentage (find the whole)
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Quick answer: To find a percentage of a number, multiply the number by the percentage and divide by 100. For example, 15% of 80 is 80 × 15 ÷ 100 = 12. Use the first row above for any numbers.
How to use the percentage calculator
Each row answers a different question. Change the numbers in the boxes and the answer at the end of the row updates as you type. Decimals and negative numbers work too.
Percentage formulas explained
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | Y × X ÷ 100 | 15% of 80 = 12 |
| X is what % of Y? | X ÷ Y × 100 | 30 is 25% of 120 |
| Percentage change from A to B | (B − A) ÷ A × 100 | 50 to 65 = +30% |
| Increase Y by X% | Y × (1 + X ÷ 100) | 200 + 25% = 250 |
| Decrease Y by X% | Y × (1 − X ÷ 100) | 200 − 25% = 150 |
| X is P% of what? | X ÷ P × 100 | 45 is 30% of 150 |
Percentage change vs percentage points
If an interest rate goes from 4% to 5%, it rose by 1 percentage point, but by 25% in relative terms, because 1 is a quarter of 4. News reports mix these up often. Use row 3 for the relative change and simple subtraction for percentage points.
Everyday percentage examples
- Discounts: a $60 jacket at 30% off costs 60 × 0.7 = $42. Use row 4 with “decreased by”.
- Tips: a 20% tip on a $45 bill is $9 (row 1).
- Sales tax or GST: $100 plus 18% tax is $118 (row 4, “increased by”).
- Price before tax: if $118 includes 18% tax, the price before tax was 118 ÷ 1.18 = $100.
- Exam scores: 42 out of 50 is 84% (row 2).
- Growth: website visits up from 1,200 to 1,500 is a 25% increase (row 3).
A common percentage mistake
A 50% drop followed by a 50% rise does not bring you back to the start. 100 down 50% is 50, and 50 up 50% is only 75. To undo a 50% fall you need a 100% rise. Percentages are always taken from the current number, not the original one.
Working with dates instead? Try our days between dates calculator.
FAQ
How do I calculate a percentage of a number in my head?
Find 10% by moving the decimal point one place left, then scale it. 10% of 80 is 8, so 5% is 4 and 15% is 12.
How do I work out a percentage increase?
Subtract the old number from the new one, divide by the old number and multiply by 100. Row 3 does it for you.
Is X% of Y the same as Y% of X?
Yes. 8% of 50 is 4, and 50% of 8 is also 4, a handy shortcut.
How do I calculate percentages in Excel?
Use =A1*B1/100 for X% of Y, or =A1/B1 formatted as a percentage for “what percent”.
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