Percentage Calculator
Three ways to work with percentages, each calculating live as you type. Find the percentage of a number, what percent one value is of another, or the increase and decrease between two figures.
What is a percentage?
A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin per centum, meaning "by the hundred." When you say 25%, you mean 25 out of every 100, or one quarter. Because every percentage shares the same denominator, percentages make it easy to compare quantities that would otherwise be awkward to weigh against each other — a score of 18 out of 24 and 30 out of 40 are both 75%, instantly comparable once converted.
This calculator handles the three percentage questions that come up most often in everyday life, and each one updates the moment you change a number so you can experiment freely.
Calculating the percentage of a number
This is the classic "find the part" question: you know the whole and a percentage, and you want the amount that percentage represents. Divide the percentage by 100 to turn it into a decimal, then multiply by the number.
Worked example — 20% of 80
This is the calculation behind sales tax, a tip on a restaurant bill, the interest earned on savings in a year, or the amount knocked off in a "20% off" sale.
Working out what percent one number is of another
Here you have two raw numbers — a part and a whole — and you want to know the part's share as a percentage. Divide the part by the whole, then multiply by 100.
Worked example — 25 is what percent of 200
Use this for turning a test score into a grade, finding what proportion of a budget a single expense takes up, or expressing how much of a goal you've completed.
Percentage increase and decrease
Percentage change measures how much a value has grown or shrunk relative to where it started. Subtract the old value from the new value, divide that difference by the old value, then multiply by 100. A positive result is an increase; a negative result is a decrease.
Worked example — from 80 to 120
A key detail people often miss: percentage change is not symmetric. Going from 80 to 120 is a 50% increase, but going back from 120 to 80 is only a 33.3% decrease — because the starting point (the denominator) is different each time.
Where percentages show up
- Shopping — work out the real saving on a discount, or add sales tax to a price.
- Finance — interest rates, loan repayments, investment returns, and tips.
- School & study — grades, proportions, probability, and word problems.
- Business — profit margins, growth rates, conversion rates, and reporting.
- Health — body-fat percentage, nutrition labels, and daily value figures.
Quick reference
Frequently asked questions
How do I calculate a percentage by hand?
Turn the percentage into a decimal by dividing it by 100, then multiply by the number. For example, 15% of 60 is 0.15 × 60 = 9. To go the other way and find what percent one number is of another, divide and multiply by 100: 9 ÷ 60 × 100 = 15%.
How do I find a percentage discount?
Multiply the original price by the discount percentage to get the amount saved, then subtract it from the price. A 30% discount on $80 saves 0.30 × 80 = $24, leaving a sale price of $56. You can also multiply directly by 0.70 (100% − 30%) to get $56 in one step.
How do I add a percentage to a number?
Multiply the number by the percentage and add the result, or multiply by 1 plus the decimal. To add 8% tax to $50: 50 × 1.08 = $54. To add a 20% tip to a $45 bill: 45 × 1.20 = $54.
Why isn't a percentage increase the same as the decrease back?
Because the base value changes. Increasing 100 by 50% gives 150. Decreasing 150 back to 100 is only a 33.3% drop, since the decrease is measured against 150, not 100. Percentage change always depends on what you start from.
How do I convert a fraction or decimal to a percentage?
For a decimal, multiply by 100 and add a percent sign: 0.45 becomes 45%. For a fraction, divide the top by the bottom first, then multiply by 100: 3/8 = 0.375 = 37.5%.
Is this percentage calculator free to use?
Yes. Every calculation runs instantly in your browser, there's nothing to install or sign up for, and the numbers you enter are never sent to a server.
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