How to calculate percentages
A percentage is simply a fraction of 100 — the word comes from the Latin per centum, “per hundred.” Almost every percentage question is one of three types, and this calculator covers all three. Enter your numbers above for an instant answer, or follow the worked examples below to do it by hand.
1. Percent of a number
To find X% of a number, multiply the number by X and divide by 100. Example: 15% of 200 = 200 × 15 ÷ 100 = 30. This is the everyday case — a tip, a commission, a portion of a total.
2. What percent one number is of another
Divide the part by the whole and multiply by 100. Example: 45 is 45 ÷ 180 × 100 = 25% of 180. Use this for “what score did I get?” or “what share of the budget is this?”
3. Percentage change (increase or decrease)
Subtract the old value from the new value, divide by the old value, and multiply by 100. Example: from 120 to 150 is (150 − 120) ÷ 120 × 100 = +25%. A positive result is an increase; a negative one is a decrease.
Quick reference: common percentages
| Percentage | Of 50 | Of 200 | Of 1,000 |
|---|---|---|---|
| 5% | 2.5 | 10 | 50 |
| 10% | 5 | 20 | 100 |
| 15% | 7.5 | 30 | 150 |
| 20% | 10 | 40 | 200 |
| 25% | 12.5 | 50 | 250 |
Mental math shortcuts
To find 10%, move the decimal one place left (10% of 240 = 24). For 1%, move it two places (1% of 240 = 2.4). Build others from those: 20% is 10% doubled, 5% is 10% halved, 15% is 10% plus 5%. And a handy trick — X% of Y equals Y% of X, so if 18% of 50 looks hard, flip it to 50% of 18 = 9.
The classic mistake: percentage points vs. percent
If an interest rate rises from 4% to 6%, that’s an increase of 2 percentage points — but a 50% increase in the rate (2 ÷ 4 = 50%). News headlines mix these up constantly. When a base value is itself a percentage, say “percentage points” for the absolute gap and “percent” for the relative change.
Where you’ll use this
Percentages run through everyday money: a tip on a restaurant bill, a discount at the register, sales tax, a grade on a test, or the growth of an investment over time. Master the three cases above and almost every real-world percentage question becomes a ten-second calculation.
Frequently asked questions
How do I calculate a percentage increase?
Subtract the original number from the new number, divide the result by the original number, then multiply by 100. From 120 to 150 is (150-120)/120 x 100 = 25% increase. A negative result means a decrease.
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100. For example, 45 out of 180 is 45/180 x 100 = 25%.
How do I add a percentage to a price?
Multiply the price by (1 + percentage/100). Adding 8% tax to $50 is 50 x 1.08 = $54. Our discount & sales-tax calculator does this automatically.
What's the difference between percentage points and percent?
A rise from 4% to 6% is 2 percentage points but a 50% increase in the rate itself. Use 'percentage points' for the absolute gap between two percentages and 'percent' for the relative change.
What is a quick way to calculate 15%?
Find 10% by moving the decimal one place left, then add half of it again. For 80: 10% is 8, half of that is 4, so 15% is 12.
Is X% of Y the same as Y% of X?
Yes — they're always equal. So 18% of 50 equals 50% of 18, which is 9. Flipping the numbers often makes the mental math easier.