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Percentage Calculator
Three percentage problems, one tool. Pick a mode below.
Please fill in both numbers.
How to use each mode
The three buttons at the top switch between the three questions people actually ask about percentages. The first, % of a number, answers things like "what is 20% of 80?" — useful for tips, discounts, and tax. The second, X is what % of Y, works backwards: you know two numbers and want the percentage between them, like "18 correct answers out of 25 is what percent?" The third, % change, measures how much a value grew or shrank, which is how you describe a price rise, a pay increase, or a drop in your electricity bill.
Pick the mode that matches your question, type the two numbers, and press Calculate. The answer appears instantly, along with a plain-language sentence explaining what it means.
The math behind percentages
A percentage is simply a fraction out of one hundred. "Per cent" is Latin for "per hundred," so 25% literally means 25 out of 100, or 0.25 as a decimal. Every percentage calculation is a small rearrangement of that one idea.
To find a percent of a number, convert the percentage to a decimal and multiply: 20% of 80 becomes 0.20 × 80 = 16. To find what percent one number is of another, divide the part by the whole and multiply by 100: 16 out of 80 is 16 ÷ 80 × 100 = 20%. And to find a percentage change, take the difference, divide by the starting value, and multiply by 100: a rise from 50 to 65 is (65 − 50) ÷ 50 × 100 = 30%.
Worked example: a sale price
A jacket costs $120 and is marked 30% off. Using mode one, 30% of 120 is 0.30 × 120 = $36, so you save $36 and pay $84. If instead you saw the jacket drop from $120 to $84 and wanted to know the discount percentage, mode three gives (84 − 120) ÷ 120 × 100 = −30%, confirming the 30% cut.
Percentage vs. percentage points
This distinction quietly causes real confusion, especially in news headlines. If an interest rate moves from 4% to 6%, that is a rise of 2 percentage points. But in relative terms it is a 50% increase, because 2 is half of the original 4. Both statements are true; they just measure different things. When precision matters — in finance, statistics, or polling — say "percentage points" for the plain gap and "percent" for the relative change.
Frequently asked questions
How do I find a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 20% of 80 is 0.20 × 80 = 16. Use the first mode above.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value, then multiply by 100. From 50 to 65 is (65−50)/50 × 100 = 30% increase. Use the third mode.
What is the difference between percentage and percentage points?
A percentage point is the plain difference between two percentages. Going from 10% to 15% is a rise of 5 percentage points, but a 50% relative increase.
Can this calculator do reverse percentages?
Yes. Use the second mode: if 16 is the part and 80 is the whole, it tells you 16 is 20% of 80.