Percentage Calculator
Percent of a number, percentage change, and adding or removing a percentage — with the working shown.
What is X% of Y?
30
20 ÷ 100 × 150 = 30
X is what percent of Y?
25%
30 ÷ 120 × 100 = 25%
Percentage change (increase or decrease)
25% increase
(100 − 80) ÷ |80| × 100 = 25%
Add or subtract a percentage
287.5
250 + 15% = 287.5
212.5
250 − 15% = 212.5
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Every Everyday Percentage Question in One Place
Percentages come up in discounts, tips, tax, exam marks, pay rises and price changes. Most questions are one of four kinds, and each has its own formula. This calculator gives you all four side by side and shows the working, so you get the answer and the method.
How to Calculate a Percentage
- Pick the question. Choose the calculator that matches what you want to know: percent of a number, what percent, percentage change, or adding a percentage.
- Type your numbers. Enter the two values. The answer updates as you type.
- Read the working. Each result shows the formula with your numbers in it, so you can check it or copy the method.
The Four Formulas
- X% of Y = X ÷ 100 × Y
- X as a percent of Y = X ÷ Y × 100
- Change from A to B = (B − A) ÷ |A| × 100
- Y plus X% = Y × (1 + X ÷ 100), and Y minus X% = Y × (1 − X ÷ 100)
Frequently Asked Questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 20% of 150 is 20 ÷ 100 × 150 = 30.
How do I work out what percent one number is of another?
Divide the part by the whole and multiply by 100. For example, 30 out of 120 is 30 ÷ 120 × 100 = 25%.
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. Going from 80 to 100 is (100 − 80) ÷ 80 × 100 = a 25% increase. A negative result is a decrease.
How do I add a percentage to a number?
Multiply the number by 1 plus the percentage as a decimal. Adding 15% to 250 is 250 × 1.15 = 287.5. To subtract 15%, multiply by 0.85 instead, which gives 212.5.
Why isn't a 50% increase undone by a 50% decrease?
Because each percentage is taken from a different starting value. 100 increased by 50% is 150, but 50% of 150 is 75, so decreasing by 50% leaves 75, not 100.