Sports Betting Odds, Implied Probability & Vig
Convert prices into probabilities and understand how sportsbook margin changes the break-even point.
Odds tell you both the potential payout and the break-even probability implied by that price. Sportsbook margin appears when the implied probabilities across mutually exclusive outcomes add to more than 100%.
Decimal odds
Implied probability is approximately 1 ÷ decimal odds. Decimal 2.00 corresponds to 50% before considering the full market pricing.
American odds
Positive American odds show profit on a $100 stake; negative odds show the stake required to win $100. Both can be converted to decimal odds and implied probability.
Market overround
If a two-way market is priced at 1.91 / 1.91, each side implies about 52.36%, for a total of roughly 104.72%. The amount above 100% is the raw overround.
Break-even thinking
If you repeatedly take decimal 1.91, you need to win more than about 52.36% of those wagers to break even before other costs.
Prediction versus price
Believing an outcome is more likely is not enough. A bet only has positive expected value under your estimate if the offered price is favorable relative to that probability.
No-vig is a model, not a discovered truth
Proportionally normalizing implied probabilities is a transparent way to remove displayed margin, but other margin-allocation models are possible. The result should be called a no-vig estimate rather than an objective probability.
Compare equivalent settlement rules
Before comparing prices, verify that overtime treatment, push rules, listed pitchers/players, dead-heat treatment or other settlement conditions define the same market.
Reproduce a worked example
The sportsbook dataset stores example prices with raw implied probability, full market percentage, overround and normalized probabilities. Use it to check the formulas rather than relying on a detached percentage.