📊 Understanding Betting Odds: A Complete Guide
Master the fundamentals of betting odds to identify profitable arbitrage opportunities
Understanding betting odds is fundamental to successful sports betting and arbitrage opportunities. This comprehensive guide will transform you from a beginner to an odds expert, helping you spot profitable opportunities instantly.
The Three Main Types of Odds
1️⃣ Decimal Odds (European)
Most popular worldwide and easiest to understand
- Used in Europe, Australia, Canada, and New Zealand
- Shows total payout including your stake
- Simple calculation: Payout = Stake × Odds
- Always greater than 1.00
📝 Example: Decimal Odds
Odds: 2.50
Stake: $100
Total Payout: $100 × 2.50 = $250
Profit: $250 - $100 = $150
2️⃣ Fractional Odds (British)
Traditional format used in UK and Ireland
- Shows profit relative to stake
- Written as fraction: 5/2, 7/4, 1/3
- First number = potential profit
- Second number = stake required
📝 Example: Fractional Odds
Odds: 5/2
Stake: $20
Profit: ($20 × 5) ÷ 2 = $50
Total Return: $20 + $50 = $70
3️⃣ American Odds (Moneyline)
Standard format in USA
- Positive (+) for underdogs, Negative (-) for favorites
- Based on $100 stake or $100 profit
- Positive: Shows profit on $100 stake
- Negative: Shows stake needed to win $100
📝 Example: American Odds
Underdog (+200):
Stake: $100 → Profit: $200 → Total: $300
Favorite (-150):
Stake: $150 → Profit: $100 → Total: $250
Quick Visual Comparison
Same Probability
2.50
Decimal
Same Probability
3/2
Fractional
Same Probability
+150
American
Odds Conversion Table
| Decimal |
Fractional |
American |
Implied Probability |
| 1.50 |
1/2 |
-200 |
66.67% |
| 2.00 |
1/1 (Evens) |
+100 |
50.00% |
| 2.50 |
3/2 |
+150 |
40.00% |
| 3.00 |
2/1 |
+200 |
33.33% |
| 4.00 |
3/1 |
+300 |
25.00% |
| 5.00 |
4/1 |
+400 |
20.00% |
Conversion Formulas
// Decimal to Fractional
Fractional = (Decimal - 1) expressed as fraction
Example: 2.50 → (2.50 - 1) = 1.5 = 3/2
// Fractional to Decimal
Decimal = (Numerator ÷ Denominator) + 1
Example: 5/2 → (5 ÷ 2) + 1 = 3.50
// American to Decimal
If positive: Decimal = (American ÷ 100) + 1
If negative: Decimal = (100 ÷ |American|) + 1
Example: +200 → (200 ÷ 100) + 1 = 3.00
Example: -150 → (100 ÷ 150) + 1 = 1.67
// Decimal to American
If Decimal ≥ 2: American = (Decimal - 1) × 100
If Decimal < 2: American = -100 ÷ (Decimal - 1)
Calculating Implied Probability
🎯 Why Implied Probability Matters
Implied probability converts odds into a percentage chance of an outcome occurring. This is crucial for:
- Identifying value bets (when true probability > implied probability)
- Spotting arbitrage opportunities (when combined probabilities < 100%)
- Understanding bookmaker margins
- Making informed betting decisions
// From Decimal Odds
Probability = (1 ÷ Decimal Odds) × 100
// From Fractional Odds
Probability = Denominator ÷ (Numerator + Denominator) × 100
// From American Odds
If positive: Probability = 100 ÷ (American + 100) × 100
If negative: Probability = |American| ÷ (|American| + 100) × 100
🔥 Spotting Arbitrage Opportunities
When the sum of implied probabilities from different bookmakers is less than 100%, you've found an arbitrage opportunity!
Example: Player A @ 2.10 (47.62%) + Player B @ 2.05 (48.78%) = 96.40% = 3.6% guaranteed profit!
Interactive Odds Calculator
💡 Pro Tip: Using Odds Knowledge for Arbitrage
Now that you understand odds formats and implied probability, you can quickly spot arbitrage opportunities. Look for situations where different bookmakers offer odds that create a combined probability under 100%. This is exactly what ArbZoom's AI does automatically across thousands of markets!
Common Betting Terms Explained
Even Money
2.00 (Decimal)
1/1 (Fractional)
+100 (American)
Win equals your stake
Odds-On Favorite
1.50 (Decimal)
1/2 (Fractional)
-200 (American)
Win less than stake
Long Shot
10.00 (Decimal)
9/1 (Fractional)
+900 (American)
High risk, high reward
