What is X% of Y?
X is what percent of Y?
Percentage change from X to Y
Percentages turn up everywhere — discounts, exam scores, tax, interest and growth figures. This calculator solves the three most common percentage questions side by side, updating as you type.
How to use the Percentage Calculator
- 1 Pick the question that matches your problem — each box is a separate calculator.
- 2 Type your two numbers; decimals and thousands separators are fine.
- 3 Read the answer instantly and copy it with one click.
Formula
X% of Y = (X ÷ 100) × Y X is what % of Y = (X ÷ Y) × 100 % change = (New − Old) ÷ |Old| × 100
Worked examples
Input: Percentage 15, value 200
Result: 30
0.15 × 200 = 30
Input: X = 30, Y = 200
Result: 15%
30 ÷ 200 × 100 = 15%
Input: Old 50, new 75
Result: +50%
(75 − 50) ÷ 50 × 100 = 50% increase
What is a percentage?
A percentage is a number expressed as a fraction of 100 — "per cent" literally means "per hundred". 25% means 25 out of every 100, or 0.25 as a decimal. Converting between the two forms is the key to every percentage calculation: divide a percentage by 100 to get a decimal multiplier, or multiply a decimal by 100 to get a percentage.
How to calculate the percentage of marks
To find your percentage of marks, divide the marks you obtained by the total marks and multiply by 100. Use the second calculator ("X is what % of Y"): enter your obtained marks as X and the total marks as Y.
| Marks obtained | Total marks | Percentage |
|---|---|---|
| 425 | 500 | 85% |
| 912 | 1,100 | 82.91% |
| 38 | 50 | 76% |
| 1,050 | 1,200 | 87.5% |
For several subjects, add up the marks of all subjects first, then divide by the sum of their maximum marks: averaging the subject percentages gives the wrong answer when the subjects have different totals.
Percentage change vs. percentage points
If an interest rate moves from 4% to 5%, it has risen by 1 percentage point but by 25 percent (because 1 is 25% of 4). Use the third calculator for relative change and simple subtraction for percentage-point change.
Tips for mental maths
- 10% of any number: move the decimal point one place left.
- 5% is half of 10%; 20% is double it.
- X% of Y always equals Y% of X — so 8% of 50 is the same as 50% of 8, which is 4.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 18% of 250 = 0.18 × 250 = 45.
How do I work out what percentage one number is of another?
Divide the part by the whole and multiply by 100. 45 out of 60 is 45 ÷ 60 × 100 = 75%.
How do I calculate my percentage of marks?
Divide your obtained marks by the total marks and multiply by 100. For example, 425 out of 500 is 425 ÷ 500 × 100 = 85%.
Why is a 50% increase followed by a 50% decrease not zero?
Because each percentage applies to a different base. 100 + 50% = 150, but 150 − 50% = 75. The decrease is calculated on the larger number.
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