Percentage calculator
Four percentage questions answered at once, each with its own boxes: a percent of a number, what percent, percentage change, and increase or decrease.
Free · no signup Runs in your browser
How do I calculate a percentage?
To find a percentage of a number, multiply the number by the percentage and divide by 100: 15% of 80 is 15 × 80 ÷ 100 = 12. To find what percent one number is of another, divide the part by the whole and multiply by 100. To find a percentage change, subtract the old value from the new, divide by the old value and multiply by 100. This page does all of these as you type.
The four questions
Almost every percentage problem is one of four questions. 'What is 15% of 80?' multiplies the number by the rate. '12 is what percent of 80?' divides the part by the whole. 'What is the percentage change from 50 to 65?' compares the difference with the starting value. And 'what is 80 increased by 15%?' multiplies by 1.15, while a decrease multiplies by 0.85.
The common mistakes come from using the wrong base. A rise of 50% followed by a fall of 50% does not return to the start: 100 rises to 150 and then falls to 75, because the second percentage is taken from the bigger number. Percentage points are different from percentages: a rate going from 4% to 6% is up 2 percentage points but up 50%. The original-value line at the bottom answers the reverse question, such as the price before a 15% increase: it divides by 1.15 and does not subtract 15% from the new price.
It runs in your browser. The numbers you enter are never sent anywhere.
When to use it
- Working out a discount, a tip or a share
- Finding what fraction one number is of another
- Measuring growth or decline between two values
- Checking an increase or decrease applied to a price
Mistakes it helps you avoid
- Using the new value as the base for a percentage change.
- Subtracting a percentage from a price that already includes the increase.
- Mixing percent with percentage points.
- Dividing by 100 twice.
The formula
How the answer is worked out.
X% of Y = X ÷ 100 × YX is what percent of Y = X ÷ Y × 100percentage change from X to Y = (Y − X) ÷ |X| × 100Y increased by X% = Y × (1 + X ÷ 100); decreased = Y × (1 − X ÷ 100)original before a change = new value ÷ (1 ± X ÷ 100)
A percentage change from zero is undefined, so the tool shows n/a. The sign of the change is kept: a fall shows as a negative percentage. Results are rounded for display at six decimal places and the calculation uses full precision.
Example: a sale price
A coat costs $80 and is 15% off.
- 15% of 8015 ÷ 100 × 80 = 12
- 80 decreased by 15%80 × 0.85 = 68
- Change from 80 to 68(68 − 80) ÷ 80 × 100 = −15%
The discount is $12 and the sale price is $68
Sales tax is then added to the sale price.
Terms on this page
- Percentage point
- The arithmetic difference between two percentages, such as 4% to 6% being 2 points.
- Base
- The number a percentage is taken of.
Common questions
How do I find a percentage of a number?
Multiply the number by the percentage and divide by 100. 15% of 80 is 15 × 80 ÷ 100 = 12.
How do I calculate percentage change?
Subtract the old value from the new, divide by the old value and multiply by 100.
How do I find the original price before a discount?
Divide the sale price by 1 minus the discount: $68 ÷ 0.85 = $80.
Is anything I enter sent to a server?
No. The calculation happens in your browser and nothing you type leaves your device.
What is the difference between percent and percentage points?
Going from 4% to 6% is a rise of 2 percentage points, but a 50% increase in the rate.
Where these numbers come from
- Wikipedia — Percentage What a percentage is and how to calculate with it.
- Wikipedia — Relative change and difference The formula for percentage change.
Last verified 2026-10-25 The method on this page is checked against the sources above at least once a year. Spotted something out of date? Tell us and we will fix it.
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