In-play odds are betting odds that a bookmaker keeps updating during a match, using live data, down to the result of the next ball, the next point or the next goal. Betting during a match is called in-play betting, or live betting. The software that sets these odds is the pricing part of sportsbook software.
Odds start from a probability, which is the chance that a result will happen. A pricing model is a program trained on thousands of past matches. It works out the probability of each result from the state of the match. Live sports data gives the model the state of the match, ball by ball, within a second or two of each event. The model turns each probability into odds. Then the bookmaker shortens the odds slightly, so that a winning bet pays a little less than the fair amount. This difference is the bookmaker's margin.
Imagine a Test match at Lord's, in London, at the start of the 40th over. A bookmaker offers a bet on that over: will the batting side score 6 runs or more? The model looks at the score, the batters, the bowler and the age of the ball, and gives this a 40% chance. Fair odds would be 1 ÷ 0.40, which is 2.50. The bookmaker offers 2.30 instead, to keep its margin. A bettor in London stakes £10 at 2.30. If 6 or more runs come in the over, he receives £23.
Then the first ball of the over is hit for four. The model now gives 6 or more runs in the over a 75% chance. While the new data is arriving, the bet is suspended for a few seconds, and no bets are accepted. Otherwise, a person at the ground, who saw the ball before the data arrived, could bet on a result that had already happened. When the bet reopens, the odds have fallen to 1.25. For the same reason, in-play bets are held for a few seconds before they are accepted.
A big match can have hundreds of such bets open at once, all priced by the model. So the speed of the data feed matters more than almost anything else. The bookmaker also limits how much it accepts on each result, through sportsbook risk management.
Fast, repeated betting during a match is a known risk for problem gamblers. So regulators watch in-play betting closely, under the rules of responsible gambling. In-play betting on sport is legal in Britain. In India, all online betting is banned, and the Online Gaming Act 2025 bans every online game played for money.