How to use: Calculate percentages for common scenarios. Select Type: "Percentage of Number" (find X% of Y), "Percent Change" (increase/decrease between values), or "What Percent" (find what % X is of Y). Enter Value 1 and Value 2 based on type. Examples: 20% of 150 = 30. Percent change from 100 to 120 = 20% increase. 30 is what % of 150 = 20%. Applications: sales tax (6% of $50 = $3), discounts (25% off $80 = $60 final), tip calculations (15% of $40 = $6), grade calculations, financial growth rates, population changes. Formula: Percentage = (part/whole) × 100. Essential for shopping, finance, statistics, and everyday math.