Quick Answer
To calculate the percentage of a number, divide the percentage by 100 and multiply the result by the number. For example, to find 20% of 150, calculate 20 ÷ 100 = 0.20, then multiply 0.20 × 150 = 30. Therefore, 20% of 150 is 30.
P% of N = N × P ÷ 100So when someone asks how do you calculate the percentage of a number, the basic rule is always the same: convert the percentage to a decimal and multiply by the number. The rest of this guide explains why that works and shows you how to apply it quickly in any situation.
Percentage of a Number Formula
N = the original number
P = the percentage
P% of N = N × P/100
The word percent literally means "per hundred." So 20% means 20 per 100, which is the same as the fraction 20/100 = 0.20. When you write "20% of 150," the word of means multiply. So the full calculation is 0.20 × 150 = 30.
What is 20% of 150?
Write the percentage: 20%
Convert to decimal: 20 ÷ 100 = 0.20
Multiply by the number: 0.20 × 150 = 30
✅ 20% of 150 = 30
Percentage Calculator
Find P% of N — Interactive Calculator
Want to check more calculations without doing the arithmetic yourself? The Percentage Calculator handles any percentage problem instantly — including "what percentage is X of Y" and percentage increase/decrease.
How Do You Calculate the Percentage of a Number Step by Step?
Every percentage calculation follows three steps, regardless of what numbers are involved.
Write the percentage
Identify the percentage figure you need to find. For example: 15%.
Divide the percentage by 100
This converts it from a percentage to a decimal. 15 ÷ 100 = 0.15. You can also move the decimal point two places to the left: 15% → 0.15.
Multiply by the number
0.15 × 80 = 12. Therefore, 15% of 80 = 12. That is the complete calculation.
How to Convert a Percentage to a Decimal
Converting a percentage to a decimal is the only tricky part of this calculation. The rule is simple: divide by 100, or equivalently, move the decimal point two places to the left.
| Percent | Divide by 100 | Decimal |
|---|---|---|
| 0.5% | 0.5 ÷ 100 | 0.005 |
| 1% | 1 ÷ 100 | 0.01 |
| 5% | 5 ÷ 100 | 0.05 |
| 10% | 10 ÷ 100 | 0.10 |
| 15% | 15 ÷ 100 | 0.15 |
| 20% | 20 ÷ 100 | 0.20 |
| 25% | 25 ÷ 100 | 0.25 |
| 50% | 50 ÷ 100 | 0.50 |
| 75% | 75 ÷ 100 | 0.75 |
| 100% | 100 ÷ 100 | 1 |
| 125% | 125 ÷ 100 | 1.25 |
5% converts to 0.05, not 0.5. The decimal point moves two places, not one. So 5% of 300 = 0.05 × 300 = 15, not 0.5 × 300 = 150.
Three Ways to Calculate a Percentage of a Number
Method 1 — The Decimal Method
This is the standard approach. Convert the percentage to a decimal, then multiply.
Example: 35% of 240
35 ÷ 100 = 0.35
0.35 × 240 = 84
Method 2 — Direct Formula
Multiply the percentage and the number together first, then divide by 100.
Example: 35% of 240
35 × 240 = 8,400
8,400 ÷ 100 = 84
Both methods give the same answer. Method 1 is usually faster by hand. Method 2 sometimes works better when percentages are awkward decimals.
Method 3 — The Fraction Method
Certain percentages have clean fraction equivalents that make the arithmetic very quick.
| Percentage | Fraction | Example |
|---|---|---|
| 50% | 1/2 | 50% of 90 = 90 ÷ 2 = 45 |
| 25% | 1/4 | 25% of 200 = 200 ÷ 4 = 50 |
| 75% | 3/4 | 75% of 80 = 3 × (80 ÷ 4) = 60 |
| 20% | 1/5 | 20% of 350 = 350 ÷ 5 = 70 |
| 10% | 1/10 | 10% of 450 = 450 ÷ 10 = 45 |
| 12.5% | 1/8 | 12.5% of 160 = 160 ÷ 8 = 20 |
How to Calculate Percentages Without a Calculator
These shortcuts let you work out common percentages in your head. Each one builds on the idea that 10% of a number is just that number divided by 10.
Percentage of a Number — Ten Worked Examples
The examples below cover a range of percentages, including values below 1% and above 100%. All answers are verified.
Percentages can exceed 100%. Example 9 shows that 125% of 80 = 100, meaning the result is larger than the original number. There is no rule that percentages must stay between 0 and 100.
Real-World Applications
Discount
Discount: 25%
0.25 × 80 = $20 off
Final price: $80 − $20
Sales Tax
Tax rate: 8%
0.08 × 120 = $9.60 tax
Total: $120 + $9.60
Tip
Tip: 20%
0.20 × 60 = $12 tip
Total: $60 + $12
Commission
Rate: 6%
0.06 × 5,000
Survey Result
42% selected option A
0.42 × 800
These are two different things. "25% of $80" = $20 (the discount amount). "$80 after a 25% discount" = $60 (the final price). The percentage calculation gives you the amount taken off, not the amount you pay.
Percentage of a Number vs. Other Percentage Problems
There are three different percentage questions that look similar but require different formulas. Mixing them up is one of the most common mistakes.
For the third question, use the Percentage Change Calculator to handle percent increase and decrease calculations automatically.
Common Percentage Mistakes
| Mistake | Wrong | Correct |
|---|---|---|
| Forgetting to divide by 100 | 20 × 150 = 3,000 | 20/100 × 150 = 30 |
| Converting 5% to 0.5 | 5% = 0.5 | 5% = 0.05 |
| Using the wrong formula | 20% of 150 → 20/150 × 100 | 20% of 150 → 150 × 0.20 |
| Confusing discount amount with final price | 20% off $100 = $20 (final price) | 20% off $100 → $20 off, pay $80 |
| Thinking percentages can't exceed 100% | 125% is not possible | 125% of 80 = 1.25 × 80 = 100 |
| Rounding too early | Round each step separately | Keep full precision until the final answer |
Practice Problems
Work through these before checking the answers. Each one uses the same three-step method described above.
Shortcut: divide 340 by 10.
Shortcut: 96 ÷ 4 = 24.
10% of 220 = 22; 5% = 11; 15% = 33.
10% of 180 = 18; 5% = 9.
1% = 4; 0.5% = 2; total = 6.
100% = 64; 25% = 16; total = 80.
Shortcut: 160 ÷ 8 = 20.
1% of 800 = 8; 0.25% = 8 ÷ 4 = 2.
Frequently Asked Questions
Key Takeaways
How Do You Calculate the Percentage of a Number — Summary
- The formula is: P% of N = N × P/100. Divide the percentage by 100, then multiply by the number.
- 20% of 150 = 0.20 × 150 = 30. This is the core example for the entire method.
- The word "of" in a percentage problem means multiply.
- 5% = 0.05, not 0.5. Moving the decimal two places is essential.
- Percentages can exceed 100%. 125% of 80 = 100.
- Mental math: 10% = divide by 10; 5% = half of 10%; 20% = double 10%; 25% = divide by 4.
- Finding the percentage of a number and finding percentage change are two different calculations with different formulas.
Related Pages
These pages from Statistics Fundamentals cover closely related topics in probability, statistics, and calculation.
- Statistics and Probability — the main category this article belongs to.
- Percentage Calculator — calculate any percentage instantly online.
- Percentage Change Calculator — find percent increase or decrease between two values.
- Basic Probability — percentages appear throughout probability as relative frequencies.
- Probability Rules — probability and percentage share the same 0-to-1 scale.
- Descriptive Statistics — percentages appear in summaries, relative frequencies, and data descriptions.
- Percentiles — a related but distinct concept from percentage.
- Statistics Formulas — reference sheet for core statistical and mathematical formulas.