Sports betting: odds, margin and markets
This guide is mostly about the casino game catalogue and slot mechanics; the betting pages cover the basic ideas without tips and without operator figures. For the main subject, see the games page and the slots page.
Odds formats
Decimal odds show the total return per unit staked, stake included: 2.50 returns 2.50 for every 1 bet. Fractional odds, common in some countries, show the profit relative to the stake: 3/2 means 3 profit for every 2 staked, the same as 2.50 in decimal. American odds use positive and negative numbers around 100. The format changes, the meaning does not.
Implied probability
Dividing 1 by the decimal odds gives the implied probability: 2.50 corresponds to 40%. It is the bookmaker's estimate of the chance of that outcome, adjusted for its margin.
The margin
Add the implied probabilities of every outcome in a market and the total exceeds 100%. The excess is the bookmaker's margin, the betting equivalent of the house edge. It is the same idea as RTP on a slot, seen from the other side: the higher the margin, the less the market returns on average.
| Idea | Betting | Slots |
|---|---|---|
| What the operator keeps | Margin built into odds | 100% minus RTP |
| Where to see it | Sum of implied probabilities | Game information panel |
| Who sets it | The operator | The operator, from the studio's configurations |
Pre-match and in-play
Pre-match bets are placed before the event; in-play bets during it, with odds that move constantly. In-play betting has a rhythm close to slots: fast decisions and many bets in little time. The same rule applies — set the budget first.
Sport guides
- Bet types: singles, accumulators, systems.
- Football
- Tennis
- Basketball
- Cricket
Why the margin matters for slot players too
Once you can read the margin in a set of odds, you also understand why a 94% slot and a 96% slot are not equivalent over the long run, even though either can win or lose in a single session. In both cases the operator builds an edge into the product, and in both cases you can find it before you play: in the odds for betting, in the information panel for games.
Odds, markets and limits are set by the operator and change constantly. Sports betting law varies by country; check that the operator is licensed where you live.