Percentage Calculator
Percent means “per hundred”, so 15% is just 15/100 = 0.15, and “15% of 200” is 0.15 × 200 = 30. That single idea covers most percentage questions; the four modes here package the common ones so you do not have to remember which number goes on top.
The four calculations
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | (X ÷ 100) × Y | 15% of 200 = 30 |
| X is what % of Y? | (X ÷ Y) × 100 | 30 of 200 = 15% |
| % change X → Y | ((Y − X) ÷ X) × 100 | 80 → 100 = +25% |
| Price after X% off | Y × (1 − X ÷ 100) | $80 − 25% = $60 |
The mistakes people make
Percent change is not symmetric: going from 80 to 100 is a 25% rise, but 100 back to 80 is a 20% fall. Stacked percentages do not add either – two successive 10% discounts leave you paying 81%, not 80%. And “percentage points” differ from “percent”: a rate moving from 4% to 5% is up one percentage point, but a 25% increase. For adding a tip or tax, use the “X% of Y” mode and add it on.
Related tools
To express a result as a fraction instead – “0.375 is 3/8” – use the fraction to decimal converter. For body-composition percentages the BMI calculator is purpose-built.
FAQ
How do I calculate 15% of 200?
Multiply 200 by 0.15: 200 × 0.15 = 30.
How do I calculate percent change?
Subtract the old value from the new, divide by the old, multiply by 100. From 80 to 100: (100 − 80) ÷ 80 × 100 = 25% increase.
How do I calculate a discount?
Multiply the price by (1 − discount/100). $120 at 30% off: 120 × 0.7 = $84.
Why do two 10% discounts not equal 20% off?
The second 10% comes off the already-reduced price. 100 → 90 → 81, so the total discount is 19%.
What is the difference between percent and percentage points?
If a rate goes from 4% to 5%, that is 1 percentage point, but a 25% relative increase. The two are often confused in news headlines.