Percentage Calculator
Type in a percentage and a number and you get the answer straight away, whether you are splitting a bill, checking a discount or helping with homework.
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The formula
Part = (Percentage / 100) x Whole. To find the percentage instead: Percentage = (Part / Whole) x 100.
How to calculate a percentage
A percentage is just a fraction out of 100. So "15 percent" means 15 out of every 100, or 0.15. To find 15% of 240, you multiply 240 by 0.15 and get 36.
The calculator above does the same thing, and it can also run the sum the other way round. Pick "X is what percent of Y?" if you know the two numbers and want the percentage, or "X is Y% of what number?" if you know the part and the percentage but not the total.
A worked example
Say a jacket costs 80 and the shop takes 25% off. 25% of 80 is 80 x 0.25 = 20, so you save 20 and pay 60.
A quick way to check your answer is to round. 25% is a quarter, a quarter of 80 is 20. If the calculator says something wildly different, you have probably typed a number in the wrong box.
Mental maths shortcuts
- 10%: move the decimal one place left. 10% of 340 is 34.
- 5%: take 10% and halve it.
- 1%: move the decimal two places left.
- 15%: add 10% and 5%. This is how most people work out a tip.
- 25%, 50%, 75%: a quarter, a half, three quarters.
Common mistakes
The most frequent slip is mixing up "percent of" and "percentage points". If an interest rate moves from 4% to 5%, it went up by one percentage point, but it rose by 25 percent in relative terms. News stories use both, so it is worth checking which one you are reading.
The second is taking a percentage of the wrong total, for example working out a discount on the sale price instead of the original price.
Examples to check
Type these into the calculator above to see how it behaves. Every result below was produced by the same calculator code that runs on this page.
| What you enter | What you get |
|---|---|
| What is X% of Y?; Percentage (%): 5; Of this number: 80 | Result: 4 |
| What is X% of Y?; Percentage (%): 12.5; Of this number: 240 | Result: 30 |
| What is X% of Y?; Percentage (%): 35; Of this number: 1250 | Result: 437.5 |
| What is X% of Y?; Percentage (%): 150; Of this number: 60 | Result: 90 |
Percentage Calculator: frequently asked questions
How do I find what percent one number is of another?
Divide the first number by the second and multiply by 100. For example, 45 out of 60 is 45 / 60 = 0.75, which is 75%. Choose "X is what percent of Y?" in the calculator to do it for you.
How do I find the original number if I only know the percentage?
Divide the part by the percentage written as a decimal. If 30 is 20% of a number, the number is 30 / 0.20 = 150.
How do I turn a percentage into a decimal?
Divide by 100, or move the decimal point two places to the left. So 15% is 0.15, 5% is 0.05 and 120% is 1.2. Multiplying by that decimal is exactly how every percentage calculation works.
Can a percentage be more than 100?
Yes. 150% of a number is one and a half times that number. Percentages above 100 show up all the time with growth: if sales went from 40 to 100, they grew by 150%.
Why does a 50% rise followed by a 50% fall not bring me back to where I started?
Because the second percentage is taken from a bigger number. Start at 100, rise 50% to 150, then fall 50% and you land on 75. The same trap catches people with investments and sale prices.
How accurate is this calculator?
It uses standard double-precision arithmetic, accurate to about 15 significant digits. Results are rounded only for display.
Last reviewed: October 3, 2026