How to use this calculator
The three calculations explained
What is X% of Y?
This mode finds a percentage of any number. It answers questions like "what is 15% of 80?" or "how much is 20% off a £60 item?"
How it works: multiply the number by the percentage, then divide by 100.
Example: What is 15% of 80? Multiply 80 by 15, then divide by 100. The answer is 12.
X is what percentage of Y?
This mode works out what percentage one number is of another. It answers questions like "40 out of 200, what percentage is that?" or "my score was 34 out of 50, what did I get?"
How it works: divide the first number by the second number, then multiply by 100.
Example: 40 is what percentage of 200? Divide 40 by 200, then multiply by 100. The answer is 20%.
What is the percentage change from X to Y?
This mode calculates how much something has gone up or down, expressed as a percentage. It answers questions like "a salary went from £32,000 to £36,500, what percentage increase is that?" or "traffic dropped from 1,200 to 900 visits, how much is that?"
How it works: subtract the original number from the new number, divide by the original number, then multiply by 100. A positive result means an increase; a negative result means a decrease.
Example: A price changes from £50 to £65. Subtract 50 from 65 to get 15. Divide 15 by 50 to get 0.3. Multiply by 100. The price increased by 30%.
Common uses for a percentage calculator
Percentages appear in more everyday situations than most people realise. Here are some of the most common reasons people use this tool:
- Working out how much you save in a sale (percent off a price)
- Calculating a tip at a restaurant
- Checking a test or exam score as a percentage
- Seeing how much a salary has increased from one year to the next
- Tracking how much weight has been gained or lost
- Measuring business revenue growth between two periods
- Comparing profit margins across different products
- Working out the percentage of a budget spent so far
Frequently asked questions
-
A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin "per centum," meaning "out of one hundred." So 25% means 25 out of every 100, or a quarter of the whole. People use percentages to compare quantities on a common scale, which makes them easier to understand than raw numbers alone.
-
For round numbers, the 10% trick is the quickest method: move the decimal point one place to the left. Ten percent of £80 is £8. From there, you can build other percentages: 20% is double that (£16), 5% is half of it (£4), and 15% is 10% plus 5% (£12). For less tidy numbers, multiplying the number by the percentage and dividing by 100 is the reliable method.
-
Percentage change is directional: it measures how much a value has moved from a starting point to an ending point, and the result can be positive (an increase) or negative (a decrease). Percentage difference is non-directional: it measures the gap between two values without treating either as the "original," and the result is always positive. Use percentage change when comparing before and after. Use percentage difference when comparing two separate things, like two prices or two salaries, where neither is the starting point.
-
The calculator uses standard mathematical formulas and produces results to two decimal places. For everyday purposes (discounts, tips, salary calculations, test scores), the results are as precise as you need. Very large numbers or very small percentages may show minor floating-point variations in the final decimal place, which is a property of how computers handle certain numbers rather than an error in the formula.
Related calculators
Need a more specific tool? These calculators handle common percentage tasks: