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Common percentages — 200

To find X% of Y, multiply Y by X and divide by 100: Result = Y × (X / 100). For example, 20% of 350 = 350 × 0.20 = 70. This is the most common percentage calculation — used for tips, discounts, tax calculations, and commission. A quick mental shortcut: to find 10%, simply move the decimal point one place left. For 10% of 250, that's 25. To find 5%, halve that (12.5). To find 15%, add the 10% and 5% results: 25 + 12.5 = 37.5. For larger percentages, use this calculator for instant accuracy.

Percentage change measures how much a value has increased or decreased relative to the original. The formula is: % Change = ((New − Old) / |Old|) × 100. If a stock price goes from $50 to $65: % Change = ((65 − 50) / 50) × 100 = +30%. If it drops from $50 to $40: ((40 − 50) / 50) × 100 = −20%. A positive result is a percentage increase; negative is a percentage decrease. Common uses include calculating price changes, salary increases, inflation adjustments, investment returns, and population growth. The calculator above handles all of these instantly.

Percentage change compares a new value to an original value and implies direction (increase or decrease). It's used when you have a before and after, like a price going from $80 to $100 (+25%). Percentage difference compares two values without implying which came first. The formula is: % Difference = (|A − B| / ((A + B) / 2)) × 100. If two stores charge $80 and $100 for the same item, the percentage difference is (20 / 90) × 100 = 22.2% — neither is the "original." Use percentage change when tracking movement over time. Use percentage difference when comparing two simultaneous values without a natural baseline.

To express X as a percentage of Y, divide X by Y and multiply by 100: (X / Y) × 100. For example, if you scored 42 out of 60 on a test: (42 / 60) × 100 = 70%. This tells you what proportion X represents of the whole Y. This calculation is used everywhere: calculating your savings rate (savings / income × 100), finding your body fat percentage, calculating what proportion of a budget you've spent, or converting test scores to percentages. The "X is what % of Y" mode in this calculator handles all these in one click.

Reverse percentage (or back-calculation) finds the original value before a percentage was applied. If a price after a 20% increase is $120, the original price was $120 / 1.20 = $100. If a price after a 15% discount is $85, the original was $85 / 0.85 = $100. The general formula: Original = Final ÷ (1 + percentage/100) for an increase, or Final ÷ (1 − percentage/100) for a discount. This is especially useful in retail (finding pre-GST or pre-tax prices), salary negotiation, and investment analysis. Our GST calculator uses this same principle for Australian tax calculations.