Sports odds represent the contract between the gambler making a bet and the casino or sportsbook. In particular, the odds specify the return you would make should the side you selected actually win the contest. Unfortunately, you usually lose your entire bet if your side loses the competition.

Sports odds themselves are typically set by a person, know as an odds-maker, book-maker or bookie. Increasingly, however, odds are set by complex computer models that analyze previous performance to make predictions on the outcome.

Traditional odds are usually expressed as a ratio, such as 4-1, which means that for every dollar you bet on the underdog, you will get $4 in return if your side wins. You can also bet on the favorite, but the return is significantly lower.

Odds may fluctuate before a contest, as other gamblers make bets. If the majority of people are betting on the underdog, for example, the odds may be changed so that the payoff for bets on the underdog is lowered. Keep in mind, however, that you lock in the odds at the moment that you place the bet irrespective of subsequent changes in the odds.

The casino or sportsbook make money by charging commissions or keeping a portion of the winnings. They make money regardless of the outcome of the competition. The sportsbook changes the odds over time to ensure that they maintain an equal ammount of money on both sides of the bet - in so doing they lock in their profit.

There are several types of odds set when betting on sports. They depend on the type of sport or occurrence within a sporting event. For example, you could place a proposition bet. This type of bet might be on which team will score the most touchdowns or run the most yards.

Another type of bet is the spread bet. In this type of bet, you are betting on one team to beat another by at least a certain amount of points. So if you bet on the underdog +7.5 points, it means that if they lose by less than 7.5 points (or if they win), you win the bet. Alternatively, if you bet on the favorite in this example, they would have to win by more than 7.5 points for you to win.

Over and under bets are also sometimes called betting on the ball or betting on the clock. With this type of bet, the odds maker states a number that is the expected total points scored by both teams. Then you choose whether you think the actual combined scores will be over or under the specified amount.