Percentage Of Number
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Percentage Calculator — All Three Percentage Questions, Solved
Every percentage problem is one of three questions: What is 15% of 240? (finding a part), 45 is what percent of 180? (finding a rate), or 36 is 15% of what? (finding the whole). Mixing up which one you're solving is where errors come from. This free calculator handles all three explicitly, shows the formula used, and answers instantly. In-browser, no signup.
The Three Forms
| Question | Formula | Example |
|---|---|---|
| What is P% of Y? | Y × P ÷ 100 | 15% of 240 = 36 |
| X is what % of Y? | X ÷ Y × 100 | 45 of 180 = 25% |
| X is P% of what? | X ÷ (P ÷ 100) | 36 at 15% → 240 |
Mental Math Toolkit
- 10% anchor: move the decimal (10% of 384 = 38.4); build others from it — 5% is half, 20% is double, 15% is one-and-a-half.
- 1% anchor: two decimal moves (1% of 384 = 3.84); scale up for odd rates like 7%.
- The swap: X% of Y = Y% of X — 8% of 50 = 50% of 8 = 4.
Where Each Form Shows Up
Finding a part: tips, taxes, commissions, discounts. Finding a rate: test scores, conversion rates, market share, progress toward goals. Finding the whole: the trap category — "the $42 deposit is 20% of the price" (price = $210), "38 attendees is 95% capacity" (capacity = 40). Reverse problems demand division by the decimal, and multiplying by mistake gives an answer that's plausibly wrong — the calculator's explicit mode selection prevents exactly that.
Free and Instant
All three forms, unlimited calculations, computed locally — a lifetime bookmark for homework, work, and shopping.