Percentages are everywhere — from shopping discounts and tax calculations to exam grades and business growth metrics. Yet many people struggle with percentage calculations, especially when they involve increases, decreases, or finding what percentage one number is of another.
In this guide, we'll cover every type of percentage calculation you'll ever need, with clear formulas and real-world examples.
What Is a Percentage?
A percentage is a way of expressing a number as a fraction of 100. The word comes from the Latin "per centum," meaning "by the hundred." When you say 50%, you're saying 50 out of every 100, or one half.
The 5 Most Common Percentage Calculations
1. Find X% of a Number
Formula: Result = Number × (Percentage ÷ 100)
Example: What is 20% of 350?
350 × (20 ÷ 100) = 350 × 0.20 = 70
Use case: Calculating a 20% tip on a $350 dinner bill.
2. What Percentage Is X of Y?
Formula: Percentage = (X ÷ Y) × 100
Example: You scored 42 out of 50 on a test. What percentage?
(42 ÷ 50) × 100 = 84%
3. Percentage Increase
Formula: Increase = [(New - Old) ÷ Old] × 100
Example: Your salary went from $50,000 to $55,000.
[(55,000 - 50,000) ÷ 50,000] × 100 = 10% increase
4. Percentage Decrease
Formula: Decrease = [(Old - New) ÷ Old] × 100
Example: A product dropped from $80 to $60.
[(80 - 60) ÷ 80] × 100 = 25% decrease (discount)
5. Find the Original Number
Formula: Original = Final ÷ (1 + Percentage/100)
Example: After a 15% tax, the total is $115. What was the pre-tax price?
115 ÷ 1.15 = $100
Quick Reference Table
| Percentage | As Decimal | As Fraction | Mental Shortcut |
|---|---|---|---|
| 10% | 0.10 | 1/10 | Move decimal one place left |
| 25% | 0.25 | 1/4 | Divide by 4 |
| 33% | 0.33 | 1/3 | Divide by 3 |
| 50% | 0.50 | 1/2 | Divide by 2 |
| 75% | 0.75 | 3/4 | Multiply by 3, divide by 4 |
Calculate Percentages Instantly
Skip the mental math — use our Free Percentage Calculator for instant results:
- ✅ Calculate X% of any number
- ✅ Find percentage increase/decrease
- ✅ Determine what % one number is of another
- ✅ Reverse percentage calculations
- ✅ 100% free, no signup
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