Percentages appear everywhere — from sale discounts to tax calculations, from grade scores to investment returns. Yet many people struggle with basic percentage calculations. This guide solves all 6 common types of percentage problems with simple, memorable formulas.
Type 1: What is X% of Y? (Most Common)
Example: What is 20% of 150?
= 150 × (20 ÷ 100) = 150 × 0.20 = 30
Real-life use: Calculating a 20% tip on a $45 restaurant bill = $9 tip.
Type 2: X is What Percent of Y?
Example: 30 is what percent of 120?
= (30 ÷ 120) × 100 = 25%
Real-life use: You scored 45/60 on a test. What's your grade? = (45÷60)×100 = 75%.
Type 3: Percentage Increase
Example: Price went from $80 to $100.
= ((100−80) ÷ 80) × 100 = (20÷80) × 100 = 25% increase
Real-life use: Your salary went from $50,000 to $55,000 — that's a 10% raise.
Type 4: Percentage Decrease
Example: Price reduced from $200 to $150.
= ((200−150) ÷ 200) × 100 = (50÷200) × 100 = 25% off
Real-life use: A store advertises 30% off a $120 jacket. New price = $120 × (1−0.30) = $84.
Type 5: Percentage Change
Positive = increase, Negative = decrease
Example: Stock went from $50 to $35.
= ((35−50) ÷ 50) × 100 = −30% (a 30% loss)
Type 6: Percentage Difference
Example: Compare 80 and 100:
= |80−100| ÷ ((80+100)÷2) × 100 = 20 ÷ 90 × 100 = 22.2%
Note: Use % difference when comparing two values without a clear "original." Use % change when one value is clearly the starting point.
Real-Life Percentage Examples
| Situation | Type | Example Calculation |
|---|---|---|
| Restaurant tip | X% of Y | 18% of $55 = $9.90 |
| Sale discount | % Decrease | 25% off $80 = $60 |
| Tax calculation | X% of Y | 8.5% tax on $200 = $17 |
| Investment return | % Change | $1,000 → $1,200 = +20% |
| Test score | X is ?% of Y | 42/50 = 84% |
| Salary raise | % Increase | $50K → $54K = +8% |
Frequently Asked Questions
How do I calculate a percentage on a calculator?
For "20% of 150": type 150 × 20 ÷ 100 = 30. Or use the % button: 150 × 20% = 30. Our online percentage calculator handles all 6 types instantly.
What is the easiest way to calculate 10%?
Just move the decimal point one place to the left. 10% of $85 = $8.50. Then you can easily find 20% (double it), 5% (halve it), or 15% (10% + 5%).
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