How do I calculate a percentage?
A percentage is a fraction of 100. To find X% of a number,
multiply the number by X and divide by 100 — so 20% of 150 is
150 × 20 ÷ 100 = 30. The first row above does this as you type.
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100. For example, 30 out of 150
is 30 ÷ 150 × 100 = 20%. Use the second row for this "X is what
percent of Y" question — handy for test scores, tips, and discounts.
How do I calculate percentage increase or decrease?
Subtract the old value from the new value, divide by the old value, then
multiply by 100. Going from 150 to 180 is a
(180 − 150) ÷ 150 × 100 = +20% change. A negative result means a
decrease.
Does anything I type get uploaded?
No. Every calculation runs in your browser with plain JavaScript. Nothing is sent to a server, logged, or stored.
Common use cases
- Working out a tip or a sales-tax line on a bill.
- Turning a test score or survey result into a percentage.
- Measuring price changes, growth rates, and discounts.
- Checking margins and markups.