Percentage Calculator
What is X percent of a number.
Input sheet
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Percentages turn up everywhere money or measurement does: a tip on a dinner bill, a sales-tax line, a discount sticker, a test score. This finds the plain amount that a given percent of a number works out to.
How it works
Multiply the number by the percent divided by 100.
A percent is just a fraction out of 100. "15%" means 15 per hundred, or 0.15 as a decimal. To take a percent of something you scale the number by that decimal, which is why the math is a single multiplication.
The two common confusions are direction and base. "What is 15% of 200" (this tool) is different from "200 is 15% of what" or "what percent is 30 of 200". Make sure the number you type in the second box is the whole you are taking a slice of.
Result = percent ÷ 100 × the number
Worked examples
A 15% tip on a $200 dinner bill. → $30
15 ÷ 100 = 0.15, and 0.15 × 200 = 30.
8% sales tax on a $1,500 purchase. → $120
0.08 × 1,500 = 120, so the total with tax would be $1,620.
Tips & gotchas
- To go the other way (what percent one number is of another), divide the part by the whole and multiply by 100.
- A quick mental check: 10% is the number with the decimal moved one place left, and 5% is half of that. 15% is 10% plus 5%.
- Stacked percentages do not add. A 20% discount followed by a 10% coupon is not 30% off — it is 0.80 × 0.90 = 72% of the original, a 28% reduction.
FAQ
How do I add a percentage on top of a number?
Find the percent of the number, then add it back. For 8% tax on $50: 0.08 × 50 = $4, so the total is $54. A shortcut is to multiply by 1.08 directly.
How do I subtract a percentage, like a discount?
Take the percent off and subtract. A 25% discount on $80 is 0.25 × 80 = $20 off, leaving $60. The shortcut is multiplying by 0.75.
Why does 'percent of' use multiplication and not division?
Because a percent is already a ratio. Converting it to a decimal (dividing by 100) and multiplying scales the number by that fraction in one step.
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