How to Find X Percent of a Number (Formula, Examples, Shortcuts)

“What is 20% of 150?” shows up everywhere—shopping sales, restaurant tips, exam scores, tax estimates, and fitness goals. Percent means per hundred, so finding a percent of a number is one of the most useful math skills you can have. This guide explains the formula, shows worked examples, and points you to a free percentage calculator when you want the answer instantly.

What does “percent of” mean?

Percent = parts per 100.
20% means 20 out of every 100, or 20/100, or 0.20 as a decimal.

So “20% of 150” means: take 150, find 20 hundredths of it.

The main formula

Result = number × (percent ÷ 100)

Or, in one line:

Result = number × percent / 100

Example: What is 18% of $240?

1. Divide the percent by 100: 18 ÷ 100 = 0.18
2. Multiply: 240 × 0.18 = 43.20

Answer: $43.20 (useful for an 18% tip or tax estimate on $240).

Example: What is 35% of 80?

• 80 × (35 ÷ 100) = 80 × 0.35 = 28

Three ways to think about the same problem

1. Decimal method — Convert percent to decimal (divide by 100), then multiply.
2. Fraction method — 25% of 80 = (25/100) × 80 = (1/4) × 80 = 20.
3. 10% shortcut — Find 10% first, then scale.

The 10% shortcut (great for mental math)

10% of a number = move the decimal point one place left.

• 10% of $85 = $8.50
• 20% = double the 10% amount → $17.00
• 5% = half of 10% → $4.25
• 15% = 10% + 5% → $8.50 + $4.25 = $12.75

This is slower than a calculator for messy numbers but excellent for quick estimates.

Real-life uses

Sale price: 30% off $90

Discount = 90 × (30 ÷ 100) = $27 off
You pay: 90 − 27 = $63

Test score: 42 correct out of 50

That is a different question (“what percent is 42 of 50?”), but related:

• (42 ÷ 50) × 100 = 84%

Our percentage calculator handles both “percent of” and “what percent” modes.

Sales tax: 8.25% on $50

• 50 × 0.0825 = $4.13 tax (rounded)
• Total ≈ $54.13

Tip: 20% of $62

• 62 × 0.20 = $12.40 tip

For bill + split + tip in one step, use the tip calculator.

Common mistakes to avoid

1. Forgetting to divide by 100 — 20% of 150 is NOT 150 × 20 (= 3000). You need 150 × 0.20 = 30.
2. Confusing “percent of” with “percent increase” — “50 increased by 20%” means 50 + (20% of 50) = 60, not just 20% of 50 alone.
3. Rounding too early — In money problems, keep extra digits until the last step, then round to cents.

Percent increase vs percent of

“Percent of” gives you a part. “Percent increase/decrease” compares old vs new values.

Practice problems (with answers)

1. What is 25% of 80? → 20
2. What is 12% of $500? → $60
3. What is 7.5% of 200? → 15
4. A $120 jacket is 40% off. Discount? → 120 × 0.40 = $48
5. What is 3% of $1,000? → $30

When to use a percentage calculator

Use the tool when:

• Percents have decimals (e.g. 8.875% tax)
• Numbers are large or awkward (e.g. 17% of $2,847)
• You need percent increase/decrease, not just “percent of”
• You want to check homework or a receipt

Open the percentage calculator, choose the mode that matches your question, enter your values, and read the result.

How this connects to tipping

A tip is a percent of a number (the bill):

Tip = bill × tip% ÷ 100

So if you understand percent-of, you already understand tipping. For a dedicated bill + split workflow, see our guide How to calculate a restaurant tip or use the tip calculator.

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Bottom line: To find X percent of a number, multiply the number by X and divide by 100. For speed and multiple question types, use the free percentage calculator.