Calcolatore di Percentuale — Formula

How Percentage Calculations Work

A percentage is a number out of 100. When someone says "20% of 500," they mean 20 out of every 100 units, applied to 500. Multiply 500 by 20, divide by 100, and you get 100. That's the core of every percentage calculation.

The Three Types of Percentage Problems

Finding a percentage of a number: X% of Y = (X * Y) / 100. Example: 15% of 80 = 12.

Finding what percentage one number is of another: (Part / Whole) * 100. Example: 25 is what percent of 200? Answer: (25/200) * 100 = 12.5%.

Finding the whole when you know a part and percentage: Whole = Part / (Percentage / 100). Example: 30 is 20% of what? Answer: 30 / 0.20 = 150.

When You'd Use This

Tipping at a restaurant, calculating a sale discount, figuring out tax on a purchase, checking what share of your income goes to rent, grading tests, or splitting a bill. Percentages show up constantly in finance, shopping, cooking, and school.

Where People Go Wrong

Confusing percentage increase with percentage of. A 20% increase on 100 gives you 120 (not 20). The increase is 20, but the result is 120.

Percentage decrease traps. If something goes up 50% and then down 50%, you don't end up where you started. $100 up 50% is $150. $150 down 50% is $75. You lost $25.

Stacking percentages incorrectly. A 10% discount plus a 20% discount is not a 30% discount. It's 10% off, then 20% off the reduced price, which equals a 28% total discount.