Understanding Sports Betting Odds: American, Decimal, and Fractional Explained

Understanding Sports Betting Odds: American, Decimal, and Fractional Explained

If you are new to sports betting, the first thing you need to understand is how odds work. Odds tell you two things: the implied probability of an outcome and how much you stand to win if your bet is correct. This guide covers the three major odds formats and how to convert between them.

American Odds (Moneyline)

American odds are the standard format used by US sportsbooks like DraftKings, FanDuel, and BetMGM. They are expressed as positive or negative numbers.

Negative odds (-): Indicate the favorite. The number tells you how much you need to wager to win $100.

• Example: -150 means you must bet $150 to win $100 in profit.

Positive odds (+): Indicate the underdog. The number tells you how much you win on a $100 wager.

• Example: +200 means a $100 bet returns $200 in profit.

Calculating implied probability from American odds:

• For negative odds: Probability = |odds| / (|odds| + 100)

• For positive odds: Probability = 100 / (odds + 100)

So -150 implies a 60% probability, and +200 implies a 33.3% probability.

Decimal Odds

Decimal odds are popular in Europe, Australia, and on prediction market platforms. They represent the total payout per $1 wagered, including your original stake.

• Example: 2.50 means a $10 bet returns $25 total ($15 profit + $10 stake).

Calculating implied probability: Probability = 1 / decimal odds

• 2.50 implies a 40% probability.

Decimal odds are the simplest format for comparing value across markets because higher odds always mean a bigger payout.

Fractional Odds

Fractional odds are traditional in the UK and Ireland. They show the profit relative to the stake.

• Example: 5/2 means for every $2 wagered, you win $5 in profit.

Calculating implied probability: Probability = denominator / (numerator + denominator)

• 5/2 implies a 28.6% probability.

Converting Between Formats

Here is a quick reference table:

| American | Decimal | Fractional | Implied Probability |

|---|---|---|---|

| -200 | 1.50 | 1/2 | 66.7% |

| -150 | 1.67 | 2/3 | 60.0% |

| -110 | 1.91 | 10/11 | 52.4% |

| +100 | 2.00 | 1/1 | 50.0% |

| +150 | 2.50 | 3/2 | 40.0% |

| +200 | 3.00 | 2/1 | 33.3% |

| +300 | 4.00 | 3/1 | 25.0% |

The Vig (Juice)

Sportsbooks make money by building a margin into the odds, called the vig or juice. In a fair market, two equally likely outcomes would each be priced at +100 (50%). But a sportsbook might price them at -110 / -110, which implies 52.4% for each side — totaling 104.8%. That extra 4.8% is the vig.

Why this matters: The lower the vig, the better the value for you. Compare odds across sportsbooks to find the best price. This is exactly what odds.guru helps you do.

Prediction Market Pricing vs. Odds

Prediction markets like Kalshi display prices as cents from $0.01 to $0.99. A contract trading at $0.65 is equivalent to:

• American odds: -186

• Decimal odds: 1.54

• Implied probability: 65%

The key difference is that prediction market prices are set by the market (no vig), while sportsbook odds include the bookmaker's margin.

Practical Tips

1. Always shop for the best odds: Even a small difference in odds adds up over time.

2. Understand implied probability: It helps you assess whether a bet offers value compared to your own estimate.

3. Use decimal format for quick comparison: It is the most intuitive for spotting the best payout.

4. Check our odds comparison tools: odds.guru displays odds from multiple platforms side by side.

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Compare odds across all major sportsbooks and prediction markets on odds.guru.