Percentage Calculator

Checked 15 October 2026. What was checked. How these pages are maintained.

Percentage formulas

Part = percent ÷ 100 × whole. Percent = part ÷ whole × 100. Percent change = (new − old) ÷ old × 100. A change from 80 to 100 is +25%.

Worked example

15% of $80 is $12. 12 is 15% of 80. A price that moves from $80 to $100 is a 25% increase: (100 − 80) ÷ 80.

A 25% decrease from $100 is $75, which is not the reverse of a 25% increase. To undo a 25% increase you divide by 1.25, not subtract 25%.

Three questions that share a word

Twelve percent of 85 is 0.12 × 85 = 10.2. That is “percent of.” Thirty-six out of 90 is 36 ÷ 90 = 0.40, so 36 is 40 percent of 90. That is “what percent.” A move from 90 down to 72 is (72 − 90) ÷ 90 = −0.20, a 20 percent decrease. That is “percent change.” The three boxes on this page are those three questions. They do not feed each other. Changing the top pair does not alter the change row.

Percent change uses the old number as the base. From 72 back to 90 is (90 − 72) ÷ 72 = 0.25, a 25 percent increase. The trip down was 20 percent and the trip back is 25 percent because the base changed. Subtracting the same percent you added will not restore the start.

Where people type the wrong base

A discount is a percent of the original price, which is the “percent of” question, and then a subtraction. A tip is the same shape. A markup is profit divided by cost. A margin is profit divided by the selling price. Those last two are on the markup and margin calculator, because putting them in a generic percent box is how a 40 percent quote gets priced at the wrong dollar. If the problem is “how many days is 15 percent of a year,” 0.15 × 365 = 54.75 days. The unit stays whatever unit you typed.

More than 100 percent, and a percent of a percent

Forty is 200 percent of 20, because 40 ÷ 20 = 2. The page will print that. It is not an error. A change from 20 to 40 is a 100 percent increase, which is a different question from “40 is what percent of 20.” People swap those and then argue with the result. A percent of a percent is another trap this form will not stack for you. Ten percent of 10 percent of 500 is not 20 percent of 500. It is 0.10 × 0.10 × 500 = 5. Run the first percent, then type that result as the new whole. The three rows do not chain. If you need a sale price after a percent off, the discount page does the subtraction. This page only answers the percent question you pointed it at.

Common questions