How do you calculate a percentage?
To find what percent one number is of another, divide the part by the whole and multiply by 100: (part ÷ whole) × 100. For example, 30 out of 150 is (30 ÷ 150) × 100 = 20%. To find a percent of a number, multiply the number by the percent and divide by 100.
A percentage expresses a number as a fraction of 100 — from the Latin per centum, "by the hundred." Whether you are working out a discount, a tip, a test score, or a price change, every percentage problem reduces to one of three core operations, and this calculator handles all three.
The three percentage calculations
1. Finding a percentage of a number
To find X% of Y, multiply Y by X and divide by 100. If a $150 jacket is 20% off, the discount is (150 × 20) ÷ 100 = $30, so you pay $120.
2. Adding or subtracting a percentage
To add tax or a tip, calculate the percentage and add it back. Adding 15% to an $80 bill gives 80 + (80 × 15 ÷ 100) = $92.
3. Calculating percentage change
Percentage change shows growth or decline relative to the start: ((new − old) ÷ old) × 100. A rise from $50 to $75 is a 50% increase.
Common percentage examples
| Question | Calculation | Answer |
|---|---|---|
| What is 10% of 250? | 250 × 10 ÷ 100 | 25 |
| What is 25% of 80? | 80 × 25 ÷ 100 | 20 |
| Add 8% tax to $45 | 45 + (45 × 8 ÷ 100) | $48.60 |
| Change from 40 to 60 | ((60 − 40) ÷ 40) × 100 | +50% |
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