How do you calculate a percentage?
The core formula: part divided by whole, times 100. Scored 42 out of 50? 42 divided by 50 is 0.84, so 84 percent. Reversed, to find 15 percent of 80: convert to a decimal, 0.15, and multiply, giving 12. Percent change: new minus old, divided by old, times 100, and the divide-by-the-original part is where most errors live.
The delightful trick worth keeping: percentages commute. X percent of Y always equals Y percent of X, so an awkward 4 percent of 75 becomes 75 percent of 4, which is obviously 3. It works because both are just x times y divided by 100.
For tips and quick estimates, build from 10 percent, which is one decimal shift: 10 percent of 64 is 6.40, so 20 percent doubles it to 12.80 and 15 percent adds half of it back for 9.60. One caution flag: a 50 percent gain does not undo a 50 percent loss, because the base changed underneath you, a fact that fuels casinos and confuses stock portfolios.
Part divided by whole, times 100. And for mental math, flip stubborn ones: x percent of y equals y percent of x, so 4 percent of 75 is just 75 percent of 4, which is 3.
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https://frequentlyaskedquestions.us/q/how-to-calculate-percentage/Everybody Asks. (2026, July 28). How do you calculate a percentage? https://frequentlyaskedquestions.us/q/how-to-calculate-percentage/“How do you calculate a percentage?” Everybody Asks, 28 July 2026, https://frequentlyaskedquestions.us/q/how-to-calculate-percentage/.“How do you calculate a percentage?” Everybody Asks. Last modified July 28, 2026. https://frequentlyaskedquestions.us/q/how-to-calculate-percentage/.This page summarizes the primary sources listed above. For academic or encyclopedic work, cite those primary sources directly wherever possible.