NBA
MLBBetting Fundamentals
How to Read a Prop Line
The number isn’t random. Someone looked at pace, role, and history, landed on a figure, and the oddsmaker wrapped it in vig. What you see — Over 274.5 at -110 — is the result. Your only job is to decide whether there’s an edge. This is how to read every piece of it.
Odds converter
Type any American price. The implied probability is what the book is charging you to win that bet — break-even, before any edge.
Read it like this: a -110 price says the book needs the bet to win 52.4% of the time just to break even. If your read says it wins more often than that, you have an edge.
The number
The line is a forecast, not a coin flip — it is the level at which the book expects the result to land roughly half the time.A passing-yards line of 274.5 is not a guess that he’ll go for exactly 274 — it’s the level the book believes splits the outcomes down the middle. Set it too high and everyone hammers the Under; set it too low and the Over gets pounded. The book’s incentive is balance, so the posted number is the most informed midpoint available at that moment.
The odds and the vig
Vigorish is the rent the book charges to take both sides; at -110 each way the house keeps about 4.8% no matter who wins.Vigorish is rent. A -110 price implies a 52.4% break-even win rate, but the true probability of a coin-flip line is 50% — that 2.4% gap on each side is the house’s cut. Across both sides the implied probabilities add to about 104.8%, and that overage is what the book keeps no matter who wins. The converter above turns any price into its break-even rate instantly.
Lower juice is free edge. A book offering -105 instead of -110 on the same number is handing you a better price for an identical opinion — which is the entire case for keeping more than one book.
The half-point
A line ending in .5 exists to kill the push — there is no way to land exactly on 24.5, so every bet resolves Over or Under.A whole number like 24 leaves room for a push — land on exactly 24 rebounds and the bet refunds. The hook (.5) removes that. It also lets the book fine-tune: moving a line from 24.5 to 25.5 is a full point of demand management, while changing the juice from -110 to -120 nudges the same number without touching it. When you see the number hold but the price shift, that’s a juice move, not a real line move.
The true probability
Strip the vig off both prices and the implied probabilities add back to 100% — that no-vig number is the market's honest estimate.De-vigging is the move: take the implied probability of each side, divide each by their sum, and you get the no-vig fair probability. For a -110/-110 market that’s 50% a side. The worked example below runs the full arithmetic. Once you have the fair number, your edge is simply your own estimate minus the fair line.
Mahomes passing yards, 274.5
Suppose the analysts who set the number looked at his season mean, the defense he is facing, the game total, and the weather, and landed on 274.5. The book posts it two ways and charges juice on both: Over 274.5 -110 and Under 274.5 -110. Here is what those prices actually say.
| Over -110 implied | 52.4% | what the price charges for the Over |
|---|---|---|
| Under -110 implied | 52.4% | what the price charges for the Under |
| Both sides add to | 104.8% | more than 100% — that overage is the vig |
| De-vigged fair Over | 50.0% | the market's honest 50/50 read |
| Book's hold | 4.5% | kept regardless of who wins |
The fair line says 274.5 is a true coin flip. Your only job from here is to decide whether your own read on Mahomes beats 50% by enough to overcome that 4.5% rent. If your model says 278, the Over has value; if it says 272, the Under does. The number was never the question — the gap between your number and the fair number is.
Game context
Injuries, matchup rank, rest, and weather move a prop before the public ever sees it — the posted number already prices most of it in.A starter ruled out can swing a teammate’s usage line several points; a back-to-back saps minutes; a top-ranked defense caps a ceiling; wind and cold flatten passing and total markets. The hard part is that the book already knows all of this. By the time a prop is public, the obvious context is priced in — the edge lives in the context the market has mis-weighted, not the context it ignored.
The line move
When the number moves against the side the public is hammering, that reverse move is the sharpest signal a prop gives you.Money typically arrives in two waves: sharp, low-volume bets early and late, and high-volume public money in the hours before lock. When a line moves toward the side the public is on, that’s just demand. When it moves againstheavy public action — reverse line movement — a smaller, sharper pool is pushing the other way, and the book is listening. That’s the tell worth tracking.
Watch moves as they happen on the sharp-money feed, and learn to read them with the sharp-money guide.
Putting it together
A prop is six things at once: a forecast, a price, a half-point that forces a decision, a hidden true probability, a context already half-baked in, and a line that moves when someone smart disagrees. Read them in order and the question stops being “will he go over?” and becomes “is the market’s number wrong, and by how much?” That second question is the only one with money in it.