What Is X Percent of Y Calculator

Two questions are built in, and the Calculate menu picks between them. It opens on What is X% of Y?.

1. For the first question, type the percentage into X (it begins at 20) and the whole amount into Y (it begins at 150).
2. Read the result: 20.00% of 150 is 30. The formula line shows X / 100 x Y with your numbers.
3. For the reverse question, change Calculate to X is what percent of Y?.
4. Now X is the part and Y is the whole. With 30 and 150, the result is 30 is 20.00% of 150.
5. Change either box to try another case. The answer updates as you type.

In the second question Y cannot be zero, because a part cannot be measured against nothing. The tool tells you if you try.

Either mode accepts decimals, so 8.25 for a tax rate or 62.5 for a half-marked score both work. The answer is shown to two decimals for a percentage and to up to four decimals for a plain number, which keeps small results readable without hiding detail.

The first question uses X / 100 x Y. The second uses X / Y x 100. They are inverses of each other, which is why 20 percent of 150 is 30 and 30 is 20 percent of 150.

Money answers are not rounded to cents by the tool, so round them yourself. For splitting a bill among several people, the tip calculator does the whole job. For a grade made of weighted parts, use the grade calculator.

There is a third question the tool does not have a mode for: finding the whole when you know the part and the percent. If 30 is 20 percent of a number, divide 30 by 0.20 to get 150. A line on the scientific calculator, written as 30 / 0.2, does it directly, and you can then confirm the answer here by asking what 20 percent of 150 is. Another trap is a percent of a percent: 50 percent of 20 percent is 10 percent, because 0.5 x 0.2 = 0.1, so do not add them.

Most everyday percentages can be done in your head by starting from 10 percent. Move the decimal point one place left, then build up. For 84:

• 10 percent of 84 is 8.4.
• 5 percent is half of that, 4.2.
• 15 percent is those two added together, 12.6.
• 25 percent is a quarter of the number, 21.

Type each pair into the calculator to confirm that your head and the tool agree. The same trick scales: 1 percent of 2,400 is 24, so 12.5 percent is 300 once you work out an eighth. Checking a mental answer against a tool is a good habit when money is involved.

A percentage can exceed 100. Entering 150 as X and 80 as Y gives 120, because 150 percent means one and a half times. Negative numbers also work as the arithmetic says they should.

This page answers a single question about one number. If you know a before and after and want the size of the move, use the percent change calculator. To work out the price after a sale, the discount calculator is shaped for it, and the VAT and sales tax calculator separates tax from the total in both directions.

Results are shown to two decimals and rounded for display. They are plain arithmetic for general information, and nothing you enter leaves your browser.

Two small cautions. First, check which number is the whole. A discount of 15 percent is 15 percent of the original price, not of the sale price, and a tip is a percentage of the bill before the tip. Second, watch units: 20 percent of 150 grams is 30 grams, and the answer always carries the same unit as Y. Writing the unit next to the answer prevents most slips with recipes, budgets and measurements.