How to Calculate Percentages: A Simple Guide with Examples
Percentages made easy — how to find a percentage of a number, work out percentage change, and calculate discounts, with worked examples and a free calculator.
Percentages come up everywhere — sales, tips, taxes, exam scores, interest, and statistics — and yet the math trips people up under pressure. Here are the three calculations you actually need, with examples you can follow.
1. Finding a percentage of a number
To find a percentage of a number, multiply the number by the percentage divided by 100.
Formula: result = number × (percent ÷ 100)
Example: What is 25% of 200? That's 200 × (25 ÷ 100) = 200 × 0.25 = 50. This is the calculation behind tips and sales tax — a 18% tip on a $60 bill is 60 × 0.18 = $10.80.
2. Finding what percentage one number is of another
Divide the part by the whole and multiply by 100.
Formula: percent = (part ÷ whole) × 100
Example: You scored 36 out of 40 on a test. That's (36 ÷ 40) × 100 = 90%. Same math tells you that 50 out of 200 is 25%.
3. Percentage change (increase or decrease)
This is the one people get wrong most often. Subtract the old value from the new value, divide by the old value, and multiply by 100.
Formula: change = ((new − old) ÷ old) × 100
Example: A price rises from $120 to $150. That's ((150 − 120) ÷ 120) × 100 = (30 ÷ 120) × 100 = 25% increase.
The classic trap: going back from $150 to $120 is not a 25% decrease — it's only 20%, because the decrease is measured against the larger starting number ($150). Always divide by where you started.
A real-world favourite: discounts
A discount combines two of these. For "30% off a $80 jacket": the saving is 80 × 0.30 = $24, so you pay 80 − 24 = $56. The amount you pay is the original price × (1 − discount), i.e. 80 × 0.70 = $56.
Skip the mental math
Once you understand the formulas, a calculator keeps you fast and error-free:
- Percentage Calculator — find a percentage of a number, or what percent one number is of another.
- Percentage Change Calculator — measure an increase or decrease between two values.
- Discount Calculator — see the sale price and how much you save.
They're free, run in your browser, and recalculate as you type. Find more on the calculator tools page.