The Extended Percentage Calculator answers the comparison questions a basic percentage tool does not: what percent one number is of another, what X percent of Y equals, how much a value changed from X to Y, and what percent one number is more or less than another. Two number fields, a grid of four mode buttons and a Calculate button; the answer shows as labeled rows under the fields, and everything runs in your browser.
The four operations and their formulas
The four buttons correspond to four formulas. "X is what % of Y" computes X divided by Y times 100 and shows a percent: 25 over 50 gives 50%. "What is X% of Y" computes X divided by 100 times Y and shows a plain number with no percent sign: 10% of 80 gives 8. "% Change from X to Y" computes (Y minus X) divided by X times 100 and returns three rows: a signed percent with a plus sign for gains, a Direction row that reads Increase or Decrease, and an Absolute Change row that is Y minus X. "X is what % more/less than Y" computes (X minus Y) divided by Y times 100; the Difference row states how many percent more or less, and 150 against 100 gives 50% more than.
Step by step: pick, enter, calculate
Pick the operation by clicking one of the four mode buttons; the two field labels change to match, like X (value) and Y (total) in the first mode, or From (X) and To (Y) in the change mode. Type both numbers and click Calculate; the result is not live, nothing updates as you type, and the calculation runs only on the button press. One behavior worth knowing: switching to another mode clears both fields and any previous result, so changing modes also resets the calculator. If a field holds text that is not a number, the calculator shows its invalid-number message; number parsing is lenient, so 5abc reads as 5.
Worked examples, including the asymmetry
Four examples lock down the behavior. What percent is 25 of 50: 50%. What is 10% of 80: 8. Percent change from 100 to 150: +50%, Direction Increase, Absolute Change 50; from 150 back to 100 it is -33.3333%, Direction Decrease, Absolute Change -50. Now the comparison mode: 150 versus 100 reads 50% more than, but 100 versus 150 reads 33.3333% less than. The gap is not a mistake, it is the base: "more than" divides the difference by the second number, 100, while "less than" divides it by 150. Same two numbers, different denominators, different answers. Edge cases: 100 versus 100 reads 0% more than, and 99 versus 100 reads 1% less than.
Rounding, and what zero does
Each result is rounded to at most four decimals, with trailing zeros stripped: 1 over 3 shows 33.3333%, 12.5% of 3 shows 0.375, and 10% of 80 shows 8, not 8.0. Three of the four operations divide by one of your numbers, and dividing by zero is refused: what-percent-of with Y at 0, a percent change that starts at 0, and a more/less comparison against 0 all show the divide-by-zero message. The exception is What is X% of Y, which multiplies and is zero-safe: 7% of 0 is 0. A percent change with no change, from 100 to 100, is +0% with Direction Increase and Absolute Change 0.
Extended versus the base Percentage Calculator
The site also has a plain Percentage Calculator, and the two overlap only partially. The base tool has five modes that transform a value: a percent of a number, increasing it by a percent, decreasing it by a percent, what percent a value is of another, and the percent change between two values. The extended tool is built around comparisons: what percent of, what percent more or less, and a change report that adds direction and absolute change to the percent. Neither is a superset. To raise 200 by 15% you want the base tool; to know that 150 is 50 percent more than 100, you want this one.
Which formula for which question
Match the question to the operation. "What percent of the class passed?" is the what-percent-of mode, passers over total. "What is 15% of 40?" is the what-is-X-percent mode. "The price went from 199 to 249, how much is that?" is the percent-change mode, and its absolute-change row also gives you the 50 in money. "How many percent is my salary more than last year?" is the more/less mode. A terminology note: a rate that goes from 4% to 6% rises by 2 percentage points but rises by 50 percent, and this calculator reports the second; when your numbers are rates, say which one you mean, because readers mix the two up often.
Client-side, and where to go next
Everything runs in your browser: the two numbers and the four operations stay on the page, nothing is sent to a server, and reloading clears the fields and the results. To apply a percent to a value, the Percentage Calculator has the increase, decrease and percent-of modes; the Discount Calculator turns a price and a discount into a sale price; the Tip Calculator adds a tip to a bill and splits it; and the percentage calculation guide works the basic formulas by hand, including why a 15% cut followed by a 15% raise does not get you back to 240.