Sports betting: odds are probabilities with a margin built in
By Kristaps Birznieks · updated October 2026
A bookmaker's price is not a prediction; it is a probability with a margin added. Once you can read odds as probabilities and calculate that margin, every market — a hockey game, a football match, a tennis set — becomes comparable. This page covers the arithmetic, in-play betting, cash out and the steps of placing a bet. We do not describe any operator's markets, limits or promotions; those are set by the operator and change.
Three ways to write the same price
Decimal odds, standard across most of Europe, show the total return per unit staked: 2.50 returns €2.50 for a €1 stake, including the stake. Fractional odds show profit relative to stake: 3/2 is the same price as 2.50. American odds use a base of 100: a positive number is the profit on a 100 stake (+150 equals 2.50), a negative number is the stake needed to win 100 (−200 equals 1.50).
| Decimal | Fractional | American | Implied probability |
|---|---|---|---|
| 1.50 | 1/2 | −200 | 66.7% |
| 2.00 | 1/1 | +100 | 50.0% |
| 2.50 | 3/2 | +150 | 40.0% |
| 4.00 | 3/1 | +300 | 25.0% |
Implied probability and the margin
Implied probability is 1 divided by the decimal odds. Add the implied probabilities of every outcome in one market and the total is always above 100%. The excess is the bookmaker's margin, also called the overround.
Example with two outcomes: a hockey moneyline at 1.90 on each side gives 52.6% + 52.6% = 105.3%, a margin of about 5.3%. Example with three outcomes: a football match at 2.40 / 3.40 / 3.00 gives 41.7% + 29.4% + 33.3% = 104.4%, a margin of about 4.4%. To estimate the fair price of an outcome, divide its implied probability by the total: 41.7% ÷ 1.044 ≈ 39.9%, which corresponds to fair odds of about 2.51 instead of 2.40.
The lower the margin, the less each bet costs you in the long run. Comparing margins on the same market is the simplest quality test of any sportsbook.
In-play betting and cash out
In-play markets update during the event. Prices move fast and margins on live markets are often higher than before kick-off; a bet can also be rejected or re-priced if the odds change while you confirm. Cash out lets you settle a bet before the event ends at a price the bookmaker offers. That price includes a margin of its own, so regular cash-outs reduce long-term return. It is a risk-management tool, not a free option.
How to place a bet
- Choose the sport, the event and the market — for example, regulation-time result or total goals.
- Add the selection to the bet slip and check the odds and the market rules.
- Enter the stake and confirm. Note the bet ID.
- Check how the market settles: whether overtime counts, what happens if a player retires or a match is abandoned.
Betting bonuses in general terms
Sportsbook promotions usually take the form of free bets, odds boosts or deposit bonuses with a minimum-odds condition. A free bet usually returns only the profit, not the stake; a minimum-odds rule excludes low-priced favourites. Any figures are set by the operator. The details are explained in Bonus terms.
Markets we cover
Bet forms — singles, accumulators, systems, handicaps and totals — are compared in Bet types. Sport-specific guides: hockey, football, basketball and tennis. The same edge logic at the casino table is in Live casino.