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Odds Calculator

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Convert between American, decimal, and fractional odds formats, and find the implied probability behind any odds.

Odds Calculator

Live
Implied probability
40.00%
Decimal
2.50
American
+150
Fractional
3/2
Implied probability does not account for the bookmaker's built-in margin ("vig"), so true probabilities are typically somewhat lower than shown.

The formulas

American to Decimal: (American/100)+1 if positive, (100/|American|)+1 if negative Decimal to American: (Decimal-1)x100 if Decimal ≥ 2, otherwise -100/(Decimal-1) Implied probability = (1 / Decimal odds) x 100
Example

American odds of +150: decimal = (150/100)+1 = 2.50, implied probability = 1/2.50 = 40%, equivalent to fractional odds of 3/2.

Step-by-step guide

  1. Choose your input format - American, decimal, or fractional.
  2. Enter the odds.
  3. Read the implied probability and the odds converted into the other two formats.

Why the "implied" probability isn't the bookmaker's true estimate

Odds are set to include a built-in margin (often called the "vig" or "juice") that guarantees the bookmaker a profit regardless of outcome - which is exactly why the implied probabilities on both sides of a two-outcome bet typically add up to more than 100%, not exactly 100%. The gap between that total and 100% represents the bookmaker's edge, meaning the "true" probability of an outcome is usually somewhat lower than the raw implied probability shown here suggests.

Common mistakes

Treating implied probability as the bookmaker's genuine assessment of the true odds - it includes their built-in margin, so it's always somewhat inflated compared to the "fair" probability.
Forgetting the sign on American odds - a positive number (like +150) means an underdog with a bigger payout per dollar, while a negative number (like -200) means a favorite requiring a bigger stake for the same profit.

Frequently asked questions

What does positive vs. negative American odds mean?

Positive odds (like +150) show how much profit a $100 bet would win. Negative odds (like -200) show how much you'd need to bet to win $100 in profit - negative odds always indicate the favored outcome.

Which odds format is most common where?

American odds are standard in the United States, decimal odds are common across Europe, Australia, and Canada, and fractional odds remain traditional in the UK and Ireland - this calculator converts freely between all three.

Is this tool for placing bets?

No - this is a general math and format-conversion tool for understanding odds you encounter elsewhere, not a betting platform, and it doesn't process any transactions.

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