Percentage Calculator Guide: Discounts, Interest, and Ratios
Percentage calculation is frequently used in shopping discounts, interest calculations, success rates, and statistics. This guide covers percentage calculation formulas and practical examples.
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Basic percentage formulas
X% of Y = X × Y / 100. E.g., 15% of 200 = 200 × 15 / 100 = 30.
Percentage change = (New - Old) / Old × 100. E.g., from 150 to 180 = (180-150)/150 × 100 = 20% increase.
Percentage increase/decrease = Old × (1 ± Y/100). E.g., 20% discount on 500 = 500 × 0.80 = 400.
Express as percentage = (Part / Total) × 100. E.g., 45/60 = 75%.
Practical examples
Shopping discount: 300 product with 25% discount → 300 × 0.75 = 225. Savings: 75.
Interest calculation: 1000 principal, 12% annual interest → 1000 × 0.12 = 120 interest. Total: 1120.
VAT calculation: 100 + 20% VAT = 120. 120 VAT-inclusive → 120 / 1.20 = 100 net.
Success rate: 45 correct / 60 questions = 75% success.
Price after discount: 20% discount on 200 → 200 × 0.80 = 160.
Common mistakes
1. Decimal point/rounding errors: Using 15 instead of 0.15 when calculating 15%.
2. Wrong percentage change: Using (New-Old)/New instead of (New-Old)/Old.
3. Double discount: 20% + 10% discount = 30% is wrong, it's 28% (0.80 × 0.90 = 0.72).
4. Confusing percentage with points: 50% and 50 points are different things.
Utilgo percentage calculator
Utilgo Percentage Calculator performs percentage calculation, percentage change, percentage increase/decrease, and more percentage operations. All run in the browser.