Step-by-step percentage formulas, real-world examples, and a free calculator — everything you need to master percentages.
Percentages are everywhere — from shopping discounts to test scores, tax rates to nutrition labels. Understanding how to calculate percentages is one of the most practical math skills you can have. This guide covers every type of percentage calculation with clear formulas and real examples.
Every percentage calculation comes down to one core formula:
Or rearranged: Part = (Percentage ÷ 100) × Whole
The word "percent" literally means "per hundred" — so 25% means 25 out of every 100. Once you internalize this, all percentage calculations become logical extensions of the same idea.
Question: What is 15% of 80?
When a value goes up, use this formula to find the percentage increase:
A $120 jacket is 30% off. Discount = 0.30 × $120 = $36. You pay $84.
You got 42 out of 50 questions right. Score = (42÷50)×100 = 84%
$85 purchase with 8% tax. Tax = 0.08×$85 = $6.80. Total = $91.80
$65 bill with 20% tip. Tip = 0.20×$65 = $13. Total = $78
$1,000 investment grew to $1,150. Return = ((1150-1000)÷1000)×100 = 15%
20% down on $350,000 home. Down payment = 0.20×$350,000 = $70,000
| Percentage | Decimal | Fraction | Quick Mental Math Trick |
|---|---|---|---|
| 1% | 0.01 | 1/100 | Move decimal 2 places left |
| 5% | 0.05 | 1/20 | Divide by 20 (or ÷2, then ÷10) |
| 10% | 0.10 | 1/10 | Move decimal 1 place left |
| 15% | 0.15 | 3/20 | 10% + 5% (half of 10%) |
| 20% | 0.20 | 1/5 | Divide by 5 |
| 25% | 0.25 | 1/4 | Divide by 4 |
| 33.3% | 0.333 | 1/3 | Divide by 3 |
| 50% | 0.50 | 1/2 | Divide by 2 |
| 75% | 0.75 | 3/4 | Multiply by 3, divide by 4 |
To find any percentage quickly, first find 1% (just move the decimal 2 places left), then multiply. Example: 7% of $450 → 1% = $4.50 → 7% = $4.50 × 7 = $31.50. This works for any percentage in your head!
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