How to use the percentage calculator
Pick the question that matches yours from the list. A percentage of a number answers things like "what is 15% of 200?". One number as a percentage of another turns a score such as 30 out of 120 into a percent. Percentage change tells you how much something rose or fell between two values. Increased or decreased by adds or removes a percentage, which is what a price rise or a pay cut does.
Open "Show the steps" under the answer to see the working, so you can do the same sum by hand next time.
The formula
- Percentage of a number:
(percent ÷ 100) × number - One number as a percent of another:
(part ÷ whole) × 100 - Percentage change:
(new − old) ÷ old × 100 - Increase by a percent:
number × (1 + percent ÷ 100). For a decrease, use a minus sign.
Worked example
A jacket costs 80 and the price goes up to 100. The change is 100 − 80 = 20. Divide by the starting price: 20 ÷ 80 = 0.25. Multiply by 100 and the price rose by 25%.
Going the other way, from 100 down to 80, is a fall of 20 ÷ 100 = 20%. The two percentages differ because each is measured against its own starting value.
Common questions
How do I work out a percentage in my head?
Find 10% by moving the decimal point one place to the left, then build from there. For 15% of 200: 10% is 20, 5% is half of that (10), so 15% is 30.
Why is a 50% rise followed by a 50% fall not back to where I started?
The fall is taken from the larger number. 100 up 50% is 150, and 50% off 150 is 75, not 100.
What is the difference between percent and percentage points?
If a rate goes from 4% to 5% it has risen by one percentage point, but by 25 percent, because 1 is a quarter of 4.