A prop bet, short for proposition bet, is a wager on something that happens inside a game rather than on who wins it. Most often it is a player prop: will this player finish with more or fewer than a stated number of points, rebounds, passing yards or strikeouts? Some props are about the game or the team instead, such as the first team to score or the total number of home runs. The common thread is that you are betting on one specific outcome, not the final score.
The two parts of every prop: the line and the price
A prop has a line and a price, and they answer different questions.
- The line is the number the stat has to clear. "Over 24.5 points" wins if the player scores 25 or more and loses on 24 or fewer. The half point is there so the bet cannot tie; a whole-number line can end in a push, where the stake is returned.
- The price (also called the odds or the juice) says what a win pays. A price of -110 means you risk 110 to profit 100. A price of +150 means you risk 100 to profit 150.
Two bets on the same line can carry different prices, and two books can post different lines for the same player. That is why the same pick can be a better or a worse bet depending on where you take it. The odds converter turns any price into the formats you will see (American, decimal and fractional) and into the probability it implies.
How break-even probability works
Every price has a break-even probability: the share of bets at that price that must win for you to finish even over many bets. For a -110 price it is 110 divided by 210, or 52.38%. For a +150 price it is 100 divided by 250, or 40%. Notice that -110 needs you to win more than half the time even though the payout looks even; the difference is the book's margin.
That margin is called the hold or the vig. If you add up the implied probabilities of both sides of a market (over -110 and under -110 gives 52.38% plus 52.38%), you get 104.76%. The extra 4.76% is the overround; as a share of that 104.76% it is a 4.55% hold. The hold and vig calculator shows it for any pair of prices, along with the no-vig price for each side.
Break-even is a fact about the price. It says nothing about whether a pick will win. To compare your own view with the market you need a probability of your own, and the expected value calculator takes that probability from you and a price and returns the average result per unit staked. If that probability is wrong, so is the answer, and a positive number is an estimate, not a promise.
Why one prop tells you so little
A single player in a single game is a small sample with a wide spread. A player projected for 24 points can score 12 or 36 on an ordinary night. A prop that has a 55% chance of clearing still loses 45 times out of 100, and a run of five losses in a row is unremarkable. This is the reason to judge a method over hundreds of bets, to size bets in units that are a small and steady share of your bankroll, and to treat any one result as noise.
What to look at before a number means anything
- The line and where it came from. Check it against more than one book; the same player is often posted at different numbers.
- The price. Work out the break-even for it. A better price lowers the bar a pick has to clear.
- The player's recent games and role. Minutes, usage and matchup change the realistic range. The Explorer shows the real game-by-game numbers for a player, and the projections page shows our estimate for tonight's slate with its record beside it.
- Whether the player is available. A prop on a player who does not play is usually voided; rules vary by book.
How StatIQ treats props
StatIQ publishes projections and prices and logs every pick before the game, with the wins and the losses, so the record can be checked by anyone. Our methodology page explains how a projection is made and how it is graded. None of it is a recommendation to bet, and none of it implies that a price will keep paying. For a sport's slate, the NBA, NFL and MLB pages list the props we cover.
If gambling stops being fun, or you are betting more than you planned, free and confidential help is available from the National Problem Gambling Helpline at 1-800-GAMBLER.