Percentage Calculator
Free percentage calculator — find X% of a number, work out what percent one number is of another, or calculate a percentage increase or decrease. Instant, works in your browser, no sign-up.
A percentage is just a fraction out of 100 — “per cent” literally means “per hundred”. This tool covers the three percentage questions that come up most often. Pick a mode above, type your two numbers (X and Y), and the answer updates as you type.
1. What is X% of Y?
Take the percentage, divide by 100 to turn it into a plain fraction, then multiply by the other number:
result = X ÷ 100 × Y
Example: 15% of 80 → 15 ÷ 100 × 80 = 0.15 × 80 = 12.
This is the everyday “how much is the discount / tip / tax” calculation: 20% off
a $45 item is 20 ÷ 100 × 45 = $9 off.
2. X is what percent of Y?
Divide the part by the whole, then multiply by 100 to express it out of a hundred:
result = X ÷ Y × 100
Example: 20 is what percent of 50? → 20 ÷ 50 × 100 = 0.4 × 100 = 40%.
If the “part” is larger than the “whole” you simply get a result above 100% —
30 is 30 ÷ 20 × 100 = 150% of 20. (The whole, Y, can’t be zero — you can’t be
a percentage of nothing.)
3. Percentage change from X to Y
Find the difference, compare it to where you started, then express that out of a hundred:
result = (Y − X) ÷ X × 100
Example: a price rising from 80 to 100 → (100 − 80) ÷ 80 × 100 =
20 ÷ 80 × 100 = 25% increase. A price falling from 250 to 200 →
(200 − 250) ÷ 250 × 100 = −20%, i.e. a 20% decrease — a negative
answer always means a decrease.
Note the asymmetry: a 50% increase followed by a 50% decrease does not bring you back to the start (100 → 150 → 75). And the starting value X can’t be zero, because the formula divides by it.
Worked examples
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What is 15% of 80?
15% of 80 = 12
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20 is what percent of 50?
20 is 40% of 50
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A price rises from $80 to $100 — what's the percentage increase?
80 → 100 is a 25% increase
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A price drops from $250 to $200 — what's the percentage decrease?
250 → 200 is a 20% decrease
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 15% of 80 is 80 × 15 ÷ 100 = 12. In the calculator, choose “What is X% of Y?”, enter 15 for X and 80 for Y.
How do I find what percentage one number is of another?
Divide the first number by the second, then multiply by 100. For example, 20 out of 50 is 20 ÷ 50 × 100 = 40%. If the first number is bigger than the second, the answer is over 100%.
How do I calculate a percentage increase or decrease?
Subtract the old value from the new value, divide the result by the old value, then multiply by 100. A change from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% (an increase). A negative result means a decrease — going from 250 to 200 is −20%, i.e. a 20% drop.
What's the difference between “percent” and “percentage points”?
They are not the same. If an interest rate goes from 10% to 15%, that is a rise of 5 percentage points, but it is a 50% increase relative to the starting value of 10%. Use the “percentage change from X to Y” mode for the relative figure (enter X = 10, Y = 15).
Why does it say the starting value or total can't be zero?
Both “X is what percent of Y?” and “percentage change from X to Y” divide by one of your numbers (Y and X respectively). Division by zero has no defined answer, so the calculator asks you for a non-zero value instead of showing nonsense.
Can I use negative numbers?
Yes. “What is X% of Y?” and “X is what percent of Y?” work fine with negatives. Percentage change also accepts them, but be aware that the result is undefined when the starting value is zero and can look counter-intuitive when the starting value is negative, because the formula divides by that starting value.