Calculators · 5 min read
How to Calculate Percentages — Easy Methods & Examples
Percentages come up in discounts, tips, taxes, grades, and statistics. Here are the most common percentage calculations with simple formulas and worked examples.
The 4 Most Common Percentage Calculations
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | (X ÷ 100) × Y | 20% of 150 = 30 |
| X is what % of Y? | (X ÷ Y) × 100 | 45 of 180 = 25% |
| % change | ((New−Old) ÷ Old) × 100 | 80→100 = +25% |
| Price after discount | Price × (1 − discount%/100) | $200 − 30% = $140 |
Mental Math Tricks
- 10% of any number → move decimal one place left: 10% of 380 = 38
- 5% → halve the 10%: 5% of 380 = 19
- 15% → 10% + 5%: 38 + 19 = 57
- 1% → move decimal two places left: 1% of 2,500 = 25
- 20% → divide by 5: 20% of 350 = 70
- 25% → divide by 4: 25% of 160 = 40
Frequently Asked Questions
(X ÷ 100) × Y. Example: 20% of 150 = (20 ÷ 100) × 150 = 30.
((New − Old) ÷ Old) × 100. A positive result is an increase; negative is a decrease.
Final Price = Original × (1 − discount%/100). Example: $200 with 30% off = $200 × 0.70 = $140.
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