Sportsbook Odds Formats: American, Decimal and Implied Probability
Convert American and decimal odds, separate profit from total return, and understand why two-sided implied probabilities can exceed100%.
Changing a sportsbook’s odds display changes the notation, not the underlying bargain. American odds describe profit against a $100 reference; decimal odds describe total return per unit staked. Converting both into implied probability helps compare prices, but that number is not an independent forecast of the event.
This guide uses operator instructions checked November 3, 2026 and independently calculated examples. It concerns ordinary fixed-odds bets that either win or lose, without a push, commission, boost or special settlement condition.
Read the sign before the number
Positive American odds show the profit on a $100 winning stake. At +150, a winning $10 bet earns $15 profit and returns $25 including the stake. Negative odds show the stake required for $100 profit: at −125, a $10 winning stake earns $8 and returns $18. The minus sign does not mean a winning bet loses money.
FanDuel’s sports betting terminology page illustrates the same distinction with −110: $11 staked produces $10 profit and $21 total return on a win. Its separate display instructions describe choosing American or decimal formats through account preferences. Check the current interface rather than assuming every product shares those settings.
Convert the price
For positive American odds A, decimal odds D = 1 + A/100. For negative odds, use the positive magnitude B: D = 1 + 100/B. Winning total return is stake × D; net profit is stake × (D − 1). A losing bet loses its stake under the simple model.
| American | Decimal, rounded | Profit on a winning $10 | Implied probability |
|---|---|---|---|
| +150 | 2.50 | $15.00 | 40.00% |
| −125 | 1.80 | $8.00 | 55.56% |
| −110 | 1.90909… | $9.09, rounded | 52.38% |
Implied probability is a break-even price
For decimal odds, implied probability is 1/D. This follows from setting the expected net result of the simple bet to zero: p × (D − 1) − (1 − p) = 0. Solving gives p = 1/D. American equivalents are 100/(A + 100) for positive odds and B/(B + 100) for negative odds.
The calculation says what win rate would break even at that price under the assumptions. It does not demonstrate that the selection actually wins that often. Display rounding also matters: −110 converts to a repeating decimal, so using a rounded 1.91 can produce a slightly different percentage.
Why a two-sided market exceeds 100%
Suppose two mutually exclusive, exhaustive outcomes are both priced at −110, with no draw or push. Each implies 110/210 = 52.38095%. Together they sum to 104.76190%; the excess above 100% is about 4.76 percentage points, commonly called overround. That is a property of the offered prices, not a guarantee of the operator’s realised profit or your loss on a particular bet.
Dividing each implied probability by their total gives 50% in this symmetric example. Such normalisation removes the arithmetic excess; it does not discover the true probabilities. Compare the same outcome and settlement conditions, then read the accepted ticket. Our settlement guide covers cases outside this simple model, while casino game odds explains a different probability-and-payout setting.
Sources and checks
- Sports Betting Terms and How to Bet · Checked 2026-11-03
- How do I change to decimal odds on FanDuel Sportsbook? · Checked 2026-11-03