Percentage calculator
To find a percent of a number, divide the percent by 100 and multiply: 15% of 80 is 12. To find what percent one number is of another, divide and multiply by 100: 30 is 25% of 120. Percent change is (new − old) ÷ old × 100: from 50 to 65 is a 30% increase.
Type in any row: each answer updates as you go.
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The four formulas
- Percent of a number: X% of Y = X ÷ 100 × Y.
- What percent: X is (X ÷ Y × 100)% of Y.
- Percent change from A to B: (B − A) ÷ |A| × 100. A positive result is an increase, a negative one a decrease.
- Increase or decrease by X%: Y × (1 + X ÷ 100) or Y × (1 − X ÷ 100).
Results are rounded to 4 decimal places (numbers below 1 keep 6 significant digits). Negative numbers are allowed in every row.
Step by step
- Pick the question. Each row answers one question: a percent of a number, what percent one number is of another, the percent change, or a number increased or decreased by a percent.
- Type the two numbers. Use any format, such as 1,250 or 12.5. Negative numbers work too.
- Read the answer. The result under the row updates as you type, rounded to 4 decimal places (numbers below 1 keep 6 significant digits).
Frequently asked questions
How do I calculate a percentage of a number?
Turn the percent into a decimal by dividing by 100, then multiply. 15% of 80 = 0.15 × 80 = 12. A shortcut for mental math: 10% of a number moves the decimal point one place left, so 10% of 80 is 8 and 5% is half of that, 4.
What is the formula for percent increase?
Percent increase = (new value − old value) ÷ old value × 100. A price that goes from 50 to 65 rose by 15, and 15 ÷ 50 × 100 = 30%. Always divide by the starting value, not the new one.
How do I calculate a percent decrease?
Use the same formula: (new − old) ÷ old × 100, which gives a negative number. From 80 to 60 is (60 − 80) ÷ 80 × 100 = -25%, a 25% decrease.
How do I work out a discount, like 25% off?
Multiply the price by (1 − 25 ÷ 100). 25% off $80.00 is 80 × 0.75 = $60.00. For sales tax it is the other way: $40.00 plus 8.25% tax is 40 × 1.0825 = $43.30.
Why doesn't a 25% increase undo a 25% decrease?
Because each percent is taken from a different starting value. 100 increased by 25% is 125, but taking 25% off 125 gives 93.75. To get back to 100 from 125 you need a 20% decrease.
What is the difference between percent change and percentage difference?
Percent change measures from a starting value: 50 to 65 is +30%. Percentage difference compares two values with no direction, dividing the gap by their average: 15 ÷ 57.5 × 100 = 26.087%. Use percent change for before and after, and percentage difference for two separate measurements.