Implied Probability Calculator — Odds to Probability Converter

Select your odds format — American, Decimal, or Fractional — then enter the odds for the bet you want to analyse. Click Calculate Implied Probability and the tool will immediately display:

• The implied probability as a percentage
• The equivalent odds in all three formats
• Your break-even win rate at those odds

American odds use negative numbers for favourites (e.g. -110) and positive numbers for underdogs (e.g. +150). Enter them with or without the sign — the calculator handles both.

Decimal odds represent the total return per unit staked, including your stake. A decimal of 2.50 means you get $2.50 back for every $1 wagered ($1 stake + $1.50 profit).

Fractional odds are common in UK horse racing. Enter the numerator and denominator separately — for 3/1 (three-to-one), enter 3 in the first box and 1 in the second. For 2/5, enter 2 and 5.

Use implied probability to quickly compare a bookmaker's line against your own assessment of the true probability. If you believe Team A has a 55% chance of winning but the implied probability in the line is only 48%, you have a potential value bet.

Implied probability answers the question: what win rate does this price assume? Each odds format has its own conversion formula.

American Odds

• Negative odds (favourite): Implied Prob = |odds| ÷ (|odds| + 100)
  Example: -110 → 110 ÷ 210 = 52.38%
• Positive odds (underdog): Implied Prob = 100 ÷ (odds + 100)
  Example: +150 → 100 ÷ 250 = 40.00%

Decimal Odds

Implied Prob = 1 ÷ decimal odds
Example: 2.50 → 1 ÷ 2.50 = 40.00%

Fractional Odds

Implied Prob = denominator ÷ (numerator + denominator)
Example: 3/1 → 1 ÷ (3 + 1) = 25.00%
Example: 2/5 → 5 ÷ (2 + 5) = 71.43%

Why implied probability exceeds 100%

When you add the implied probabilities for all outcomes of a real bookmaker market, the total will exceed 100%. This excess — called the overround or vig — is the bookmaker's built-in margin. For a standard -110/-110 spread, the overround is 104.76%, meaning the book keeps 4.55 cents of every dollar wagered on a balanced book. Use our Vig Calculator to strip this margin out and find the true fair odds.

Example 1 — American Odds: NFL Point Spread at -110

You want to bet the Kansas City Chiefs -3.5 at -110. What win rate do you need to break even?

• Formula (negative odds): 110 ÷ (110 + 100) = 110 ÷ 210 = 0.5238
• Implied probability: 52.38%
• Break-even: you must win more than 52.38% of all -110 wagers to profit long-term
• Decimal equivalent: 1.909 (you collect $1.909 per $1 staked)
• Fractional equivalent: approximately 10/11

Most recreational bettors win around 48–50% of point-spread bets, which means they are systematically losing money at -110. Even a small edge to 53–54% is enough to generate consistent profit.

Example 2 — Decimal Odds: Champions League Match at 3.40

A European sportsbook prices Manchester City to win the Champions League at 3.40 (decimal). What is the implied probability?

• Formula: 1 ÷ 3.40 = 0.2941
• Implied probability: 29.41%
• American equivalent: +240
• Fractional equivalent: approximately 12/5

If your own research suggests Manchester City has a 35% chance of winning the tournament, the true fair price should be around 2.86 (decimal) or +186 (American). At 3.40 you are getting odds better than fair value — a positive expected value (+EV) bet.

Converting Between Formats

Professional bettors are fluent in all three formats. American odds are standard at US and Canadian sportsbooks. Decimal odds dominate in Europe, Australia, and on exchanges like Betfair. Fractional odds are traditional in UK horse racing. The implied probability is the universal language — it lets you compare any two odds instantly, regardless of format.