Every posted line includes the sportsbook margin. Removing it shows what the book actually thinks the probability is, which is the number you should compare your own estimate against.
Odds format:
Add up the implied probabilities of both sides of any line and the total comes to more than 100%. That excess is the sportsbook margin, usually called the vig, the juice or the hold. On a standard -110 / -110 line each side implies 52.38%, totalling 104.76%, so the book is holding 4.76%. You are not being quoted probability, you are being quoted probability plus the house edge.
The no-vig price is the closest thing available to the market consensus probability. When you form your own estimate of a game, the honest comparison is your number against the no-vig number, not against the posted odds. If you think a team wins 56% of the time and the no-vig line says 52%, you have an edge. If you compare against the raw -110 and conclude you have an edge over 52.38%, you have fooled yourself by the width of the margin.
Convert both sides to implied probability, add them, then divide each by that total. That scales the pair back down to 100% while keeping their relationship intact. It is a proportional method, and it is the standard approach for two-way markets. For markets with more than two outcomes the same principle applies across all of them.
Hold varies by market and tells you where a book is competitive. Main lines on major sports typically carry the lowest margin, while props, alternate lines and parlays carry considerably more. If you are shopping between books, the one with the lower hold on a market is giving you more of the true price. Over a season, consistently paying a lower margin matters more than most bettors realise.
Proportional de-vigging assumes the margin is spread evenly across both sides, and it usually is not. On lopsided markets, particularly heavy favourites, books tend to load more margin onto the popular side. More sophisticated methods exist for that case. For ordinary two-way lines near even money, the proportional method is accurate enough for the decisions most bettors make.
Main lines on major sports commonly sit around 4 to 5%. Lower is better for you. Props, alternate lines and same-game parlays carry considerably more, which is a large part of why they are harder to beat.
Because the posted odds include the house edge. Comparing your estimate to the raw line means you need to beat the market and the margin at the same time without noticing you are doing it.
The same principle does, but this calculator handles two outcomes. For a three-way market, add all three implied probabilities and divide each by the total.
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