What is X% of Y?
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Percentage Change
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Percentage Calculator
Percentages come up everywhere — discounts, marks, tax rates, interest, growth rates. This calculator handles all four common percentage questions in one place, so you don't have to remember formulas.
The Four Percentage Problems
- What is X% of Y? — "What is 15% of 2500?" → 375. Used for tips, discounts, commissions.
- X is what % of Y? — "75 is what % of 200?" → 37.5%. Used for exam scores, ratios.
- X is Y% of what? — "60 is 40% of what?" → 150. Used to find the original/total value.
- Percentage change — "From 80 to 100, change = 25% increase." Used for growth rates, price changes.
Key Formulas
X% of Y = (X / 100) × Y
X is what % of Y = (X / Y) × 100
X is Y% of Z → Z = (X / Y) × 100
% Change = ((New − Old) / |Old|) × 100
X is what % of Y = (X / Y) × 100
X is Y% of Z → Z = (X / Y) × 100
% Change = ((New − Old) / |Old|) × 100
Common Mistakes
% increase then same % decrease ≠ original. A 50% increase followed by a 50% decrease gives you 75% of the original, not 100%. This trips up most people.
Percentage points vs percentages. If a rate goes from 4% to 6%, that's a 2 percentage-point increase, but a 50% increase relative to the original rate.
Frequently Asked Questions
What is 100% of something?
Exactly the original number. 100% means "the whole thing." 200% means twice the original.
Can percentage change be more than 100%?
Yes. If something triples, that's a 200% increase. If it goes from 5 to 50, that's a 900% increase.