Percentage Calculator
Select a calculation type below
What is a percentage?
A percentage is a number or ratio expressed as a fraction of 100. The word "percent" comes from the Latin per centum, meaning "by the hundred." Percentages are used to express proportions, changes, rates, and comparisons in a standardised, easy-to-understand way.
For example, saying "40% of students passed" means 40 out of every 100 students passed the test — regardless of the actual class size.
Three types of percentage calculation
- Percentage of a number — "What is 15% of 200?" Answer: 30. Used for calculating tips, discounts, and tax.
- What percent is A of B — "30 is what percent of 200?" Answer: 15%. Used for finding scores, ratios, and market share.
- Percentage change — "What is the percentage change from 80 to 100?" Answer: +25%. Used for growth rates, price changes, and performance comparisons.
Percentage formulas
| Calculation | Formula | Example |
|---|---|---|
| X% of Y | (X / 100) × Y | 15% of 200 = 30 |
| A is what % of B | (A / B) × 100 | 30 / 200 × 100 = 15% |
| % change from A to B | ((B − A) / A) × 100 | (100−80)/80 × 100 = 25% |
| % increase | ((New − Old) / Old) × 100 | Positive result |
| % decrease | ((Old − New) / Old) × 100 | Negative result |
Real-world examples
| Situation | Calculation | Answer |
|---|---|---|
| 15% tip on a $60 meal | 15% of 60 | $9.00 |
| 20% off a $150 item | 20% of 150 = 30, then 150 − 30 | $120.00 |
| Score: 45 out of 60 | 45 / 60 × 100 | 75% |
| Salary rise: $50k to $55k | (55000−50000)/50000 × 100 | 10% increase |
| 8.5% sales tax on $200 | 8.5% of 200 | $17.00 tax |
Frequently asked questions
Multiply the number by the percentage and divide by 100. For example, 20% of 350 = (20 × 350) / 100 = 70. Or simply multiply by the decimal: 0.20 × 350 = 70.
Percentage change is the general term covering both increases and decreases. A percentage increase specifically means the new value is higher than the original. A percentage decrease means the new value is lower. Both use the same formula: ((new − old) / old) × 100. A positive result is an increase; a negative result is a decrease.
Divide A by B and multiply by 100. For example, "35 is what percent of 140?" → (35 / 140) × 100 = 25%.
Yes. A percentage above 100% is perfectly valid and simply means the part is larger than the whole reference value. For example, if last year's revenue was $100k and this year's is $250k, the change is 150%.
If you know a value after a percentage change, you can find the original by dividing by (1 + the percentage as a decimal). For example, if a price of $120 already includes a 20% markup, the original price was $120 / 1.20 = $100.