How to Calculate Percentages
A percentage is a way of expressing a number as a fraction of 100 — the word comes from the Latin per centum, meaning “by the hundred.” To calculate a percentage of a number, convert the percentage to a decimal by dividing it by 100, then multiply it by the number. So 25% of 80 is 0.25 × 80 = 20.
The same relationship can be rearranged to answer the other two common percentage questions. To find what percent one number is of another, divide the part by the whole and multiply by 100. To find a percentage change, compare the difference between two values to the starting value:
Percent change = ((New − Old) ÷ Old) × 100
A jacket costs $120 and is discounted by 30%. The discount is (30 ÷ 100) × 120 = $36, so the sale price is 120 − 36 = $84. You could also compute it directly: paying 70% of the price means 0.70 × 120 = $84.
Common Percentage Values
Some percentages come up so often that it helps to know their fraction and decimal equivalents by heart:
| Percentage | Fraction | Decimal | Example: of 200 |
|---|---|---|---|
| 10% | 1/10 | 0.10 | 20 |
| 12.5% | 1/8 | 0.125 | 25 |
| 20% | 1/5 | 0.20 | 40 |
| 25% | 1/4 | 0.25 | 50 |
| 33.3% | 1/3 | 0.333… | 66.67 |
| 50% | 1/2 | 0.50 | 100 |
| 75% | 3/4 | 0.75 | 150 |
| 100% | 1 | 1.00 | 200 |
Percentage Tips and Shortcuts
- Reverse trick: X% of Y always equals Y% of X. If 8% of 50 feels hard, flip it — 50% of 8 is 4.
- Build from 10%: To find 10%, move the decimal one place left. 30% is three times that; 5% is half of it.
- Tips without a calculator: For a 20% tip, take 10% and double it. A $47 bill → $4.70 × 2 = $9.40.
- Sequential changes don't cancel: A 50% drop followed by a 50% rise doesn't get you back — 100 → 50 → 75.
In practice Reading a pay rise, an exam score and a bill increase
A salary goes from $52,000 to $55,900. That is a rise of $3,900, and (3,900 ÷ 52,000) × 100 = 7.5% — worth checking against inflation before celebrating.
A student scores 47 out of 60: (47 ÷ 60) × 100 = 78.3%. And an electricity bill that climbs from $180 to $216 has risen 20%, not "$36" — the percentage is what makes it comparable to every other rising cost.
Frequently Asked Questions
How do I calculate a percentage of a number?
Divide the percentage by 100, then multiply by the number. For example, 25% of 80 is (25 ÷ 100) × 80 = 0.25 × 80 = 20.
How do I find what percent one number is of another?
Divide the first number by the second, then multiply by 100. For example, 30 out of 120 is (30 ÷ 120) × 100 = 25%.
How do I calculate percentage increase or decrease?
Subtract the old value from the new value, divide the difference by the old value, and multiply by 100. If a price rises from $40 to $50, the increase is ((50 − 40) ÷ 40) × 100 = 25%.
What is the difference between percentage and percentage points?
Percentage points measure the simple difference between two percentages, while percentage change is relative. If an interest rate goes from 4% to 6%, it rose by 2 percentage points, but that is a 50% increase relative to the original rate.
Can a percentage be greater than 100?
Yes. A percentage over 100 simply means more than the whole reference amount. For example, 150% of 60 is 90, and a price that doubles has increased by 100%.
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The CalculatorsGuide Editorial Team. (2026). Percentage Calculator. CalculatorsGuide. Retrieved from https://www.calculatorsguide.com/math/percentage-calculator/