Percentage Calculator
Understanding Percentages: A Practical Guide
What Are Percentages?
A percentage is a way to express a number as a fraction of 100. The term comes from the Latin "per centum" meaning "by the hundred". Percentages are used everywhere:
- Finance: Interest rates, discounts, investments
- Statistics: Survey results, probability
- Everyday Life: Tips, tax rates, battery charge
Common Percentage Formulas
| Calculation Type | Formula | Example |
|---|---|---|
| What is X% of Y? | (X/100) × Y | 15% of 200 = 30 |
| X is what % of Y? | (X/Y) × 100 | 30 is 15% of 200 |
| X% increase of Y | Y + (Y × X/100) | 200 + 15% = 230 |
Practical Percentage Tips
Quick Mental Math
- 10% = Move decimal left once
- 5% = Half of 10%
- 20% = Double 10%
Common Conversions
- 1/4 = 25%
- 1/3 ≈ 33.33%
- 1/2 = 50%
Pro Tip: To calculate a restaurant tip, find 10% then multiply by 2 for 20%, by 1.5 for 15%, etc. For example, 10% of $45 is $4.50, so 20% tip would be $9.00.