Percentage calculator
Three percentage questions, each answered as you type. Every result shows the arithmetic underneath it.
- Result
- 36
- A as % of B
- 15%
- Change
- 25%
- Difference
- 60
How each calculation works
All three use the same idea: a percentage is a fraction with 100 on the bottom. The only thing that changes is which number you already know.
A percentage of a number. Move the percent to a decimal by dividing by 100, then multiply. This is the one you want for a tip, a discount, or a tax line: 20% of 85 is 0.2 x 85, which is 17.
One number as a percentage of another. Divide the part by the whole, then multiply by 100. Scoring 36 out of 240 is 36 / 240 = 0.15, so 15%. The order matters. Dividing the whole by the part answers a different question.
Percentage change. Take the difference, divide by the number you started from, then multiply by 100. The starting figure is always the base, which is why a rise and the fall that undoes it are never the same percentage.
Where people get caught out
Two traps account for most percentage errors. The first is changing the base halfway through, which is what makes stacked discounts smaller than they look: 20% off then a further 10% off is 28% off, not 30%. The second is confusing a percentage change with a move in percentage points, which is why a poll shifting from 40% to 44% gets reported as both "up 4 points" and "up 10%" without either being wrong.
Common questions
- How do I work out a percentage of a number?
- Divide the percentage by 100, then multiply by the number. 15% of 240 is 0.15 x 240, which is 36.
- What is the difference between percentage change and percentage points?
- Percentage change is relative. Going from 4% to 6% is a 50% increase. Percentage points are absolute: the same move is a rise of 2 percentage points. Use points when both figures are already percentages.
- Why does a 50% rise followed by a 50% fall not return the original number?
- Each step is applied to a different base. 100 rises by 50% to 150, then falls by 50% of 150, which is 75. Reversing a 50% rise takes a fall of 33.33%.
- Is anything I type here sent anywhere?
- No. Every figure is calculated in your browser. Nothing is uploaded, stored, or logged.