Calculate any percentage instantly — find amounts, rates, and changes.
There are four common percentage calculations, each handled by a tab above. % of Number answers "what is 15% of 80?" — multiply 80 by 0.15 to get 12. X is % of Y answers "12 is what percent of 80?" — divide 12 by 80 and multiply by 100 to get 15%. % Change answers "what is the percentage change from 50 to 75?" — subtract the old from the new, divide by the old, and multiply by 100. Increase/Decrease applies a percentage to raise or lower a starting number.
Percentages appear in virtually every area of daily life — from sales tax and restaurant tips to investment returns, exam scores, and nutrition labels. Mastering percentage calculations helps you make smarter financial decisions, interpret data accurately, and avoid being misled by statistics.
The three core percentage problems: Almost every percentage question falls into one of three categories. First, "What is X% of Y?" — for example, what is 20% of $85? (Answer: $17.) Second, "X is what percent of Y?" — for example, 34 is what percent of 200? (Answer: 17%.) Third, "X is Y% of what?" — for example, $34 is 20% of what original price? (Answer: $170.) Our calculator handles all three with separate input modes.
Percentage change and growth: Percentage change measures how much a value has increased or decreased relative to its starting point. The formula is: ((New − Old) ÷ |Old|) × 100. A stock that goes from $50 to $65 has increased by 30%. The same stock falling from $65 back to $50 represents a 23% decrease — not 30% — because the starting point is now higher. This asymmetry is why percentage gains and losses are not symmetrical.
Common percentage mistakes to avoid: One frequent error is adding percentages directly. If a price increases by 10% and then decreases by 10%, you do not end up at the original price — you end up 1% below it (100 × 1.10 × 0.90 = 99). Another mistake is confusing percentage points with percentage change. If an interest rate rises from 4% to 5%, it has increased by 1 percentage point, but by 25% in relative terms.
Percentages in finance: Interest rates are expressed as percentages, making compound interest calculations essential financial literacy. Annual Percentage Rate (APR) reflects the yearly cost of borrowing, while Annual Percentage Yield (APY) reflects actual earnings accounting for compounding. A 6% APR compounded monthly results in an APY of approximately 6.17%. Over 30 years of mortgage payments, this small difference compounds into thousands of dollars.
Quick mental percentage tricks: To find 10% of any number, move the decimal one place left. For 5%, halve the 10% result. For 25%, divide by 4. For 33%, divide by 3. For 1%, move the decimal two places left. These shortcuts let you estimate percentages instantly without a calculator for most everyday situations.