How sportsbook odds work
Understand decimal and American odds, implied probability, margin and why prices differ between sportsbooks.
Odds are prices, not predictions
A sportsbook price expresses both an estimated probability and the operator's margin. It is not a promise about what will happen. Two sportsbooks can evaluate the same event differently, manage different liabilities or update at different speeds, so their prices may diverge.
Comparing prices matters because a small difference changes the potential return. The best displayed price is useful only when the market, selection, region and account eligibility all match what you intend to use.
The three common formats
Decimal odds show the total return per unit staked, including the stake. American odds use positive and negative numbers relative to 100 units. Fractional odds show potential profit relative to stake.
- Decimal 2.50 returns 2.50 units for every 1 unit staked.
- American +150 represents 150 units of potential profit on a 100-unit stake.
- American -200 represents 100 units of potential profit for a 200-unit stake.
- Fractional 3/2 represents 3 units of potential profit for every 2 units staked.
Margin and implied probability
Converting every outcome to implied probability usually produces a total above 100%. The amount above 100% is commonly called the overround or margin. It helps explain why blindly treating the displayed price as a pure probability can be misleading.
OddsVerity calculators are educational tools. Always check the operator's final market rules, settlement policy and current price before acting.