Work out X% of Y, what percent one number is of another, and more.
Type two numbers into the percentage calculator above and choose the question you need answered: what is X% of a number, what percent one number is of another, which number a value is a given percent of, how much something rose or fell, and what you get when you add or take away a percentage. Each answer comes with the working laid out line by line, so you can check it or copy it into homework.
How to Use the Percentage Calculator
Choose the tab that matches your question, then fill in the two boxes. The answer updates as you type.
- X% of Y – enter the percentage and the number. Use it for “what is 15% of 240?”
- X is what % of Y – enter the part and the total. Use it for test scores, shares of a budget or survey results. The result also shows the answer as a fraction.
- X is P% of what – enter the part you know and the percentage it represents to find the whole.
- % Increase / Decrease – a quick check of the change between two numbers. For a full breakdown, including the multiplier and the percentage needed to get back, use the percentage change calculator.
- Add / subtract % – start with a number and add or remove a percentage of it.
Use the share button to copy a link with your numbers filled in.
Percentage Formulas
A percentage is a number out of 100, so 25% means 25 ÷ 100 = 0.25. Every tab uses one of these three rearrangements of the same formula:
- Part = Percentage ÷ 100 × Whole
- Percentage = Part ÷ Whole × 100
- Whole = Part ÷ (Percentage ÷ 100)
Percentage Examples, Step by Step
What is 15% of 240? 15 ÷ 100 = 0.15, and 0.15 × 240 = 36.
45 is what percent of 180? 45 ÷ 180 = 0.25, and 0.25 × 100 = 25%. As a fraction that is 1/4.
30 is 12% of what number? 12% as a decimal is 0.12, and 30 ÷ 0.12 = 250.
Add 20% to 85. 20% of 85 is 17, so 85 + 17 = 102. A quicker way is 85 × 1.20 = 102.
Subtract 15% from 60. 15% of 60 is 9, so 60 − 9 = 51, which is the same as 60 × 0.85.
Quick Mental Shortcuts
- 10%: move the decimal point one place left. 10% of 340 is 34.
- 5%: half of 10%. 5% of 340 is 17.
- 1%: move the decimal point two places left. 1% of 340 is 3.4.
- Swap trick: X% of Y equals Y% of X. 8% of 50 is the same as 50% of 8, which is 4.
Percentages in Everyday Life
- A bill goes up. Your phone contract rises from $45 to $49.50 a month. The increase is $4.50, and $4.50 is 10% of $45. Use “X is what % of Y” with 4.5 and 45.
- A survey result. 45 of 180 people chose option A. “X is what % of Y” gives 25%, or one in four.
- A savings goal. You want to save 15% of a $3,200 monthly salary. “X% of Y” gives $480 a month.
- Working back from a share. A team of 12 is 30% of a department. “X is P% of what” shows the department has 40 people.
Other Percentage Questions
- Comparing an old and a new value? The percentage change calculator handles increases and decreases in full.
- Comparing two values where neither is the starting point, such as two quotes? Use the percentage difference calculator.
- Know the final price and the percentage but not the starting amount? The reverse percentage calculator finds the original value.
- Working out a sale price? The discount calculator shows the saving and the final price.
- Turning test marks into a percentage? Try the marks percentage calculator.
- Measuring how far a measurement is from the true value? Use the percent error calculator.
Where Percentage Answers Go Wrong
- Using the wrong whole. “What percent of 80 is 20?” divides by 80, not by 20. The whole always goes on the bottom.
- Adding and then removing the same percentage. Adding 20% and then taking 20% away does not bring you back to the start: 100 → 120 → 96.
- Forgetting to divide by 100. 15% is 0.15, not 15.
Percentage Calculator FAQs
Can a percentage be more than 100%?
Yes. A percentage above 100 means the part is bigger than the whole you are comparing it with. 150 is 150% of 100.
How do I find a percentage of a percentage?
Multiply the two as decimals. 20% of 50% is 0.20 × 0.50 = 0.10, which is 10%.
Does it work with decimals and negative numbers?
Yes. You can enter values such as 12.5% or −40, and the working shows each step with the decimals kept.
Why does my answer have so many decimal places?
Some divisions, such as 1 ÷ 3, never end. The calculator rounds the displayed result, and the working shows the unrounded steps.
How we checked this page: every example above was worked by hand and matches what the calculator returns. The formulas are the standard part, percentage and whole relationships taught in school maths.