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The word 'percent' comes from the Latin per centum, meaning 'by the hundred', and the symbol evolved from the Italian 'per cento' - abbreviated as 'p 100' with the two circles eventually merging into the modern %. Percentages gained prominence in the 15th and 16th centuries as commerce expanded and merchants needed a standard way to express profit margins, taxes, and interest rates across different currencies and weight systems.
Percentage change deserves particular attention because it is asymmetric: a 50% increase followed by a 50% decrease does not return you to the starting value. A ยฃ100 item marked up 50% costs ยฃ150; a 50% discount on ยฃ150 brings it to ยฃ75, not ยฃ100. This asymmetry is why percentage change calculations must specify the direction and the base value, and why this tool shows the formula alongside each result.
What is X% of Y?
Used when you know the percentage and the base number. E.g. What is 20% of 80? Answer: 16. Common for calculating tips, discounts, and tax.
Result = (X รท 100) ร Y
X is what % of Y?
Used when you want to express one number as a portion of another. E.g. 15 is what % of 60? Answer: 25%. Common for test scores, market share, and ratios.
Result = (X รท Y) ร 100
Percentage Change
Measures how much a value has increased or decreased relative to its starting point. E.g. a price went from ยฃ80 to ยฃ100 - that's a 25% increase.
Change = ((New โ Old) รท |Old|) ร 100
Add / Subtract %
Adds or removes a percentage directly from a number. Useful for applying VAT, discounts, or markups. E.g. ยฃ200 + 20% VAT = ยฃ240.
Result = Y ยฑ (X% ร Y)
โจ All calculations happen locally in your browser.