Betting Odds Converter + Implied Probability — American, Decimal & Fractional

The Formula

Betting odds are converted between American, Decimal, and Fractional formats using straightforward arithmetic. The implied probability represents the bookmaker's assessment of the likelihood of an outcome occurring, before accounting for their profit margin (overround).

Variable Definitions

How to Use This Calculator

1. 1

   Select the odds format you have (American, Decimal, or Fractional).

2. 2

   Enter the odds in your chosen format. The other two formats will be calculated automatically.

3. 3

   Optionally enter a stake amount to see your potential payout and profit.

4. 4

   Review the implied probability to understand the likelihood the odds represent.

5. 5

   Compare odds across different bookmakers by converting them to a common format.

Common Applications

• Converting betting odds between American, Decimal, and Fractional formats to compare lines across sportsbooks
• Calculating potential payout and profit on a wager based on your chosen stake amount
• Determining the implied probability of an outcome to identify value bets or mispriced lines
• Understanding the bookmaker's overround (vig) across all outcomes in a betting market

All three formats express the same probability. +200 = 3.00 = 2/1, all imply a 33.3% chance. Higher positive American odds mean lower implied probability.

Understanding the Concept

Odds conversion is an essential skill for any sports bettor. Understanding how odds translate between formats allows you to shop for the best lines across different sportsbooks, regardless of the format each book uses. American odds (also called Moneyline odds) are the standard in the United States and show either how much you need to bet to win $100 (negative odds for favorites) or how much you win on a $100 bet (positive odds for underdogs). Decimal odds are the most intuitive format — simply multiply your stake by the decimal to get your total return. They are widely used in Europe, Australia, and Canada. Fractional odds are traditional in the UK and Ireland, showing the ratio of profit to stake. The implied probability is perhaps the most important derived metric: it tells you what percentage chance the odds represent. If you believe an outcome is more likely than the implied probability suggests, you have found a value bet. Professional bettors regularly convert odds to implied probabilities to identify mispriced lines. The overround (also called vig or juice) is the bookmaker's commission built into the odds. In a fair market with two equally likely outcomes, both would have implied probabilities of 50% each, summing to 100%. In reality, sportsbooks build in a margin so the probabilities sum to over 100%, typically 102—108%. This vig is how sportsbooks make their profit regardless of the outcome. Understanding these concepts is fundamental to making informed betting decisions and managing your bankroll effectively over the long term.

Frequently Asked Questions

Sources & References