Published on August 08, 2026 • Last updated August 08, 2026
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A percentage is a way of expressing a number as a fraction of 100, written with a % sign, used to describe proportions, changes, and comparisons in a standardized way.
Percentages are one of the most commonly used ways to express a proportion, because they standardize any ratio onto a scale of 0 to 100, making it easy to compare values that would otherwise be hard to relate — for example, comparing a student's score out of 40 questions to another student's score out of 75 questions. A percentage is calculated by dividing a part by a whole and multiplying by 100. Beyond the basic "part of a whole" calculation, percentages are also used to describe change over time.
Percentage increase measures how much a value has grown relative to its original amount, while percentage decrease measures how much it has shrunk — both critical for tracking things like sales growth, population change, or investment returns. A related but less obvious calculation is reverse percentage, which works backward from a known percentage and result to find the original starting value — useful, for instance, when you know a discounted price and the discount rate but need to find the original price. Percentages appear constantly in everyday contexts: retail discounts and markups, interest rates, tax calculations, exam scores, statistics, and financial reporting.
Despite this ubiquity, percentage calculations are a common source of small but consequential errors — particularly confusing percentage increase with percentage points, or forgetting that a 50% increase followed by a 50% decrease does not return a value to its original amount, since the base changes between the two calculations. Understanding percentages is foundational to interpreting nearly every other calculator on this site, from loan interest rates to tax slabs to body fat measurements — all of which express their results, at some point, as a percentage of a whole.
Learn how Percentage is calculated
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