Percentage Calculator
Work out percentages three ways: what X% of a value is, what one number is as a percentage of another, and the percentage change between two values.
What is X% of a value?
Enter the percentage and the value.
X is what percent of Y?
Enter the part and the total.
Percentage change between two values?
Enter both values.
How it works
A percentage expresses a part in relation to a whole divided into one hundred. "Per cent" literally means "per hundred". When we say 20%, we mean 20 parts out of 100 — that is, one fifth.
This calculator solves the three most common percentage questions, each in its own block, with the result appearing as you type:
- What is X% of a value? Multiply the value by the percentage and divide by 100. For example, 15% of 200 is 200 × 15 ÷ 100 = 30.
- What percent is one number of another? Divide the part by the total and multiply by 100. For example, 30 out of 200 is 30 ÷ 200 × 100 = 15%.
- What is the percentage change between two values? Subtract the starting value from the final one, divide by the starting value and multiply by 100. From 200 to 250, the change is (250 − 200) ÷ 200 × 100 = 25% increase.
You don't have to pick a mode: all three are available at once, so just fill in the block that matches your question.
When to use
Percentages are everywhere. When working out a store discount ("30% off $250, what's the price?"), checking a tip, understanding a rent or salary increase, or reading an exam result ("I got 42 out of 50, what's that as a grade?").
The third block, percentage change, is especially handy for comparing before and after: how much a price went up, how much a target grew, how much an indicator dropped. It's the same calculation you see in economic news, sales reports and tracking spreadsheets. Having all three forms together avoids the usual confusion over which number divides which.
Practical examples
Discount on a purchase
A jacket at $250 with 30% off: in the first block, 30% of 250 is $75 off. So you pay $175. A quick way to check whether a deal is what it claims to be.
Exam score
You got 42 out of 50 questions right. In the second block, 42 divided by 50 times 100 is 84%. If the exam was out of 100, that's a score of 84.
Common mistakes
The most common mistake is adding percentages from different bases as if they were the same. A 10% increase followed by another 10% doesn't make 20% — it makes 21%, because the second increase applies to a value that has already grown. Percentages don't simply add when the bases change.
Another frequent slip shows up in percentage change: increasing by 50% and then decreasing by 50% doesn't return you to the original value. If something cost 100, rises 50% to 150 and then falls 50%, it lands at 75 — not 100. The base of the second calculation is different from the first.
There's also the confusion between "increase to X%" and "increase by X%". "To 120%" means the final value is 120% of the original; "by 120%" means adding 120% to the original, reaching 220%. Reading carefully avoids errors that double (or halve) the result.
Frequently asked questions
How do I quickly calculate 15% of a value?
Multiply the value by 15 and divide by 100. Or, mentally: 10% is moving the decimal one place (10% of 200 = 20), and 5% is half of that (10). Adding them, 15% of 200 = 30.
Is a 10% increase twice the same as 20%?
No. The second increase applies to the already-increased value. Two 10% increases result in 21%, not 20%, because percentages compound rather than simply add.
How do I turn a percentage into a decimal?
Divide by 100. So 25% becomes 0.25 and 7% becomes 0.07. That decimal form is what you use in direct multiplications inside formulas.
Can percentage change be negative?
Yes. When the final value is smaller than the starting one, the change is negative, indicating a decrease. From 250 to 200, for example, there is a 20% drop.