How to work out percentages
A percentage is simply a part out of 100. Once you know the pattern, the three most common questions are easy — and this calculator handles all of them. For the full formulas and worked examples, see our guide: How to Calculate Percentage.
1. Finding a percentage of a number
Multiply the number by the percentage and divide by 100.
Example: 20% of 150 = 150 × 20 ÷ 100 = 30. Handy for tips, discounts, and taxes.
2. What percent one number is of another
Divide the first number by the second, then multiply by 100.
Example: 30 out of 150 = 30 ÷ 150 × 100 = 20%. Great for scores and “how much of the total”.
3. Percentage increase or decrease
Find the difference, divide by the original value, and multiply by 100.
Example: from 40 to 50 = (50 − 40) ÷ 40 × 100 = 25% increase. Useful for price changes and growth.
Everyday uses
- Working out a discount in a sale.
- Adding a tip or a tax to a bill.
- Turning a test score into a percentage.
- Comparing a price change before and after.