Percentage Calculator
Three quick calculators in one: find X% of a number, work out what percent one number is of another, and measure percentage increase or decrease.
1. What is X% of a number?
2. X is what percent of Y?
3. Percentage increase / decrease
How to calculate percentages
A percentage is simply a fraction of 100. The word comes from the Latin per centum, meaning "by the hundred." When you say 25%, you mean 25 out of every 100 — which is the same as the fraction 25/100 or the decimal 0.25.
Almost every percentage problem you'll meet in daily life is one of the three types above. Here are the formulas behind them:
| Question | Formula | Example |
|---|---|---|
| What is 15% of 200? | (15 ÷ 100) × 200 | = 30 |
| 30 is what % of 150? | (30 ÷ 150) × 100 | = 20% |
| Change from 80 to 100? | ((100 − 80) ÷ 80) × 100 | = +25% |
Real-life examples
Shopping discounts
A $60 jacket is 30% off. The discount is (30 ÷ 100) × 60 = $18, so you pay $42. Tip: for a quick mental estimate, find 10% first (move the decimal one place: $6) and multiply — 30% is simply 3 × $6.
Tipping at a restaurant
Your bill is $84 and you want to leave 18%. That's (18 ÷ 100) × 84 = $15.12. (We also have a dedicated tip calculator that splits the bill between friends.)
Salary raise
Your pay went from $52,000 to $56,000. The increase is ((56,000 − 52,000) ÷ 52,000) × 100 = 7.7%.
Percentage increase vs. percentage points
These two are often confused. If an interest rate rises from 4% to 6%, it increased by 2 percentage points — but by 50 percent (because 2 is half of 4). News headlines mix these up all the time, so it's a useful distinction to know.
Common mistakes to avoid
- Reversing a percentage change: a 20% drop followed by a 20% rise does not get you back to the start. $100 → $80 → $96.
- Using the wrong base: percentage change is always measured against the original value, not the new one.
- Adding percentages of different bases: 10% of your rent plus 10% of your groceries is not 20% of anything meaningful.
Frequently asked questions
How do I calculate a percentage without a calculator?
Find 10% by moving the decimal point one place left, then scale. For 35% of 80: 10% is 8, so 30% is 24, and 5% (half of 10%) is 4 — total 28.
How do I convert a fraction to a percentage?
Divide the top by the bottom and multiply by 100. For example, 3/8 = 0.375 = 37.5%.
What is a reverse percentage?
That's when you know the final value after a percentage change and want the original. If a price is $69 after a 25% discount, the original was 69 ÷ 0.75 = $92.
Can a percentage be greater than 100%?
Yes. If a value more than doubles, its increase is over 100%. Going from 40 to 100 is a 150% increase.