Percentage Calculator
Four percentage calculations in one place: percentage of a number, percentage relationship, percentage change, and finding the original value — entirely in your browser.
Answers: X is what percentage of Y?
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How percentage calculations work
X% of a number: multiply the number by X, then divide by 100.
value × percent ÷ 100
X is what percentage of Y: divide X by Y, then multiply by 100.
(part ÷ whole) × 100
Percentage increase or decrease: subtract the old value from the new one, divide by the old value, then multiply by 100. A negative result is a decrease.
((new − old) ÷ old) × 100
Find the original value: divide the known amount by the percentage it represents.
amount ÷ (percent ÷ 100)
Worked examples
18% of 5,000 is 900 — a common case for calculating a service charge or a discount.
If 450 out of 900 students passed, that's 450 is 50% of 900.
A price moving from 100 to 125 is a 25% increase; moving from 125 back to 100 is a 20% decrease — not 25%, because the base value is different each direction.
If a 25% deposit came to 500, the original amount was 500 ÷ 0.25 = 2,000.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percentage, then divide by 100. 18% of 5,000 is 5,000 × 18 ÷ 100 = 900.
How do I find what percentage one number is of another?
Divide the smaller (or relevant) number by the total, then multiply by 100. 450 out of 900 is (450 ÷ 900) × 100 = 50%.
Why is a percentage increase not just the reverse of the matching decrease?
Because the base changes. Going from 100 to 125 is a 25% increase, but going back from 125 to 100 is only a 20% decrease — the second calculation divides by 125, not 100.
How do I find the original value before a percentage was applied?
Divide the known amount by the percentage it represents, written as a decimal. If 25% of something is 500, the original value is 500 ÷ 0.25 = 2,000.
Can percentages be negative?
A percentage change can be — a negative result just means a decrease rather than an increase. A percentage of a number or a percentage relationship is normally positive unless one of the inputs itself is negative.