How betting odds work: what they are and how to use them

In tennis we follow the ATP and WTA tours every week, the Challenger and ITF events in between and the four Grand Slams, from the Australian Open to Wimbledon and the US Open. For beginners, our bet calculator shows the payout of a bet, for a single or an accumulator, in decimal, fractional or American odds. Enter how much you want to wager in total to see the stake for each outcome and the resulting profit. Our sure bets page shows a way to cover every outcome of a match across different bookmakers so that the combined odds return a profit, as long as the prices are still available when you place the bets. Our real-time data updates live scores as soon as a goal is scored, a point is won or a basket is made, and with live odds available for matches in-play, you can compare prices during a match and before it. You can check the opening odds of each bookmaker, follow the odds movement over time and compare it with the current odds, so you know how the market has reacted before you decide when to bet.

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Multiplying these probabilities by 100% gives the percentage. When probability is expressed as a number between 0 and 1, the relationships between probability p and odds are as follows. When Moneyline odds are quoted as a positive number +X, it means that a wager pays X to 100. However in many situations, the possible loss (“stake” or “wager”) is paid up front and, if the gambler wins, the net win plus the stake is returned. From local leagues to international tournaments, our website shows the top price for every outcome before you bet. OddsPortal is a free odds comparison site where you can compare betting odds from leading bookmakers on every match.

A variation of fractional odds is known as Hong Kong odds. However, not all fractional odds are traditionally read using the lowest common denominator (i.e. simplifying the fraction when possible). In either case, having won, the bettor always receives the original stake back too; so if the odds are 4/1 the bettor receives a total of £500 (£400 plus the original £100). Favoured by bookmakers in the United Kingdom and Ireland, and also non gamstop bookies common in horse racing, fractional odds quote the net profit that will be paid out to the bettor, should they win, relative to the stake. That value may be regarded as the relative probability the event will happen, expressed as a fraction (if it is less than 1), or a multiple (if it is equal to or greater than one) of the likelihood that the event will not happen.

Moneyline odds use $100 as the evens line, with either positive or negative outcomes. If you’d like a bit more guidance, we have a full guide on how fractional odds work in betting. You may also see odds expressed with the lowest number first e.g. 1/2 or 2/7. Once you understand betting odds and the differences between them, reading them becomes easy.

Basketball goes from NBA odds and the EuroLeague to domestic leagues such as the Super Lig in Turkey and the LNB in France, with prices on single games and on the outright winners. Before a bet, check the archived results and historical odds of the teams or players involved, across leagues and tournaments worldwide. The value bets page compares the odds of each bookmaker with the average odds for the same outcome, highlighting the markets where one price stands out, with the probability included.

The odds are a ratio of probabilities; an odds ratio is a ratio of odds, that is, a ratio of ratios of probabilities. In probability theory and statistics, odds and similar ratios may be more natural or more convenient than probabilities. Odds can also be expressed as a number, by dividing the terms in the ratio—in this case it is unique (different fractions can represent the same rational number). For example, “odds of a weekend are 2 to 5”, while “chances of a weekend are 2 in 7”. Implied by this definition is the fact that the probability of an event is given by the ratio of favourable outcomes to the total number of possible outcomes. If k is any positive number then X to Y is the same as kX to kY, and similarly if “to” is replaced with “in” or “for”.

They’re expressed as fractions, like 5/1 or 7/2, showing the ratio of profit to the original stake. Decimal odds make comparing bets straightforward because you’re seeing the total return value in one number. Higher numbers indicate higher potential payouts, while lower numbers signify favorites and lower returns relative to the stake. The key to understanding decimal odds is that they directly represent the total return. Decimal odds are the simplest format for many bettors, popular across Europe, Canada, and Australia. When novice bettors first realize that -125, 1.80 and 4/5 all represent the same probability, it can make them dizzy – but we’re here to lay it all out clearly.