Implied Probability from American Odds

Implied probability (break-even) from American odds

Implied probability converts betting odds into a percentage. It answers: “What win rate do I need to break even at this price?”

Formulas

American odds are either positive (+150) or negative (-110):

• Positive odds (+A): implied = 100 / (A + 100)
• Negative odds (-A): implied = A / (A + 100) (where A = abs(odds))

Examples

• +150 → 100 / 250 = 0.40 → 40.00%
• -110 → 110 / 210 ≈ 0.5238 → 52.38%
• -200 → 200 / 300 ≈ 0.6667 → 66.67%

Why implied probability matters

• Break-even math: you can’t evaluate value without knowing the required win rate.
• Comparing bets: implied probability lets you compare different odds on a common scale.
• EV baseline: if your estimated win % is higher than implied probability, EV tends to be positive.

Vig (sportsbook margin)

In a two-sided market, the two implied probabilities often add up to more than 100%. That extra percentage is the book’s margin. Example:

• Side A: -110 → 52.38%
• Side B: -110 → 52.38%
• Total: 104.76% (the extra 4.76% is the built-in margin)

That’s why “implied probability” is best read as break-even at that price, not truth.

Use it in BettorCalc

1. Enter American odds.
2. Read the implied probability as the break-even win rate.
3. If you have a separate win % estimate, switch to the EV tab.