How to Calculate a Percentage
Last updated 2026-09-11
Percentages show up everywhere — discounts, grades, statistics, tips. This guide covers the three most common percentage questions and the formula behind each.
Find X% of a number
Multiply the number by X, then divide by 100. To find 20% of 150: (150 × 20) ÷ 100 = 30.
Find what percentage one number is of another
Divide the part by the total, then multiply by 100. 45 out of 60 is (45 ÷ 60) × 100 = 75%.
Reverse a percentage
If you know a result and the percentage it represents, divide by the percentage as a decimal. If 30 is 20% of a number, that number is 30 ÷ 0.20 = 150.
Example
A student scores 42 out of 50 on a test. Percentage = (42 ÷ 50) × 100 = 84%.
Important Considerations
- Percentages can exceed 100% — for example, when describing growth.
- For money, round to 2 decimal places to avoid compounding rounding errors.
- Don't confuse a percentage change with a percentage point difference — they measure different things.
Frequently Asked Questions
- What's the difference between a percent and a percentage point?
- A percentage point is the simple arithmetic difference between two percentages. Going from 50% to 55% is a 5 percentage point increase, but a 10% relative (percentage) increase, since 5 is 10% of 50.
- Can a percentage be negative?
- Yes — a negative percentage represents a decrease, such as a temperature drop or a loss on an investment.
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