Percentage of a Number Calculator
What is 15% of 240? What percentage is 36 of 150? 450 is what percent of 600? These look like three different questions — they’re the same formula rearranged. Enter any two values and get the answer with full step-by-step working.
Last updated: April 2026
What is X% of a number?
Enter a percentage and a number to find the result. For example: what is 20% of 150?
X is what percentage of Y?
Enter two numbers to find what percentage the first is of the second.
Find the whole: X is P% of what number?
Enter a value and a percentage to find the total it represents a percentage of.
The three core percentage formulas
Every percentage problem is one of three types, each with its own formula. All three are handled by the calculator above.
1. Find X% of a number
Formula: Result = Number × (Percentage ÷ 100). What is 20% of 150? 150 × 0.20 = 30. This is the most common type — used for calculating tips, discounts, tax amounts, and commission.
2. Find what percentage X is of Y
Formula: Percentage = (X ÷ Y) × 100. What percentage is 30 of 150? (30 ÷ 150) × 100 = 20%. Use this to find a test score as a percentage, a market share, or how much of a budget has been spent.
3. Find the whole when you know a part and a percentage
Formula: Whole = Part ÷ (Percentage ÷ 100). 30 is 20% of what number? 30 ÷ 0.20 = 150. This is useful when you know a VAT amount and the rate and need to back-calculate the original price — the same logic the sales tax calculator uses to remove tax from a gross price.
Real-world examples
These three formulas cover the vast majority of everyday percentage questions:
| Scenario | Type | Calculation | Answer |
|---|---|---|---|
| Sales tax on $120 at 8.5% | X% of Y | $120 × 0.085 | $10.20 tax |
| 45 out of 300 survey respondents | X is what % of Y | (45 ÷ 300) × 100 | 15% |
| $400 saved = 25% of goal | Find the whole | $400 ÷ 0.25 | $1,600 goal |
| Tip on $85 bill at 18% | X% of Y | $85 × 0.18 | $15.30 tip |
| Score of 38 out of 50 | X is what % of Y | (38 ÷ 50) × 100 | 76% |
Percentage of a number vs percentage change
These are related but different operations. “What is 20% of 80?” asks for a portion of a fixed value (16). “What is a 20% increase from 80?” asks for the new value after adding 20% (96). For the second type — comparing two values or finding an increase or decrease — use the percentage change calculator. For salary increases specifically, the salary raise calculator breaks down the result annually, monthly, weekly, and hourly.
Mental estimation tricks
For quick mental calculations: 10% of any number is just moving the decimal one place left. 5% is half of 10%. 25% is dividing by 4. 33% is dividing by 3. To find 15% of $48: 10% is $4.80, half of that is $2.40, so 15% = $7.20. To find 12.5% of $160: that’s an eighth of the number, so $160 ÷ 8 = $20. Building from anchor percentages like these is almost always faster than formal calculation for round numbers.
Percentage of a percentage
When a percentage is applied to another percentage, multiply the two decimals. A sales commission of 8% on a $400 order where only 60% of the order qualifies: 8% of 60% = 0.08 × 0.60 = 0.048 = 4.8% effective rate. $400 × 0.048 = $19.20 commission. This comes up in tax calculations (a 5% state tax on top of a 3% county tax isn’t 8% combined), discount stacking, and tiered commission structures.
Finding the whole from a part and a percentage
If you know that a number is X% of some unknown whole, the whole is: Whole = Part ÷ (Percentage ÷ 100). You scored 42 points, which is 70% of the total available: 42 ÷ 0.70 = 60 total points. A store paid $34 for an item after a 15% trade discount: $34 is 85% of the list price, so list price = $34 ÷ 0.85 = $40. This reverse calculation appears constantly in tax, discount, and commission contexts.
Percentages in everyday finance
Interest rates, tax rates, investment returns, discounts, tips, and commissions are all percentage calculations. A credit card charging 24% APR on a $3,000 balance: monthly interest = $3,000 × (24 ÷ 12) ÷ 100 = $3,000 × 0.02 = $60/month. A 7% investment return on $5,000: $5,000 × 0.07 = $350 gain per year. Understanding which direction the percentage flows — whether you’re finding a part, finding the whole, or finding the rate — is the key skill that makes all these calculations straightforward.
Frequently asked questions
20% of 50 = 50 × 0.20 = 10. Mental shortcut: 10% of 50 is 5, so double it for 20% = 10. This works for any number — find 10% first, then double.
15% of 200 = 200 × 0.15 = 30. Quick method: 10% of 200 is 20, and 5% is half of that (10), so 15% = 20 + 10 = 30. This anchor approach works for any number.
(45 ÷ 180) × 100 = 25%. You can also spot this directly: 45 is exactly one quarter of 180, and one quarter is always 25%. The formula is: (part ÷ whole) × 100.
5% of 1,000 = 1,000 × 0.05 = 50. Mental shortcut: 10% of 1,000 is 100, and 5% is half of that: 50. For any number, 5% = half of 10%.
200 × 0.35 = 70. Quick method: 10% of 200 is 20, so 30% is 60, plus 5% (10) = 70.
(18 ÷ 72) × 100 = 25%. You can also notice that 18 is one quarter of 72, so it is 25%.
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