Look at a game priced -110 on both sides. Each price implies a 52.4% chance, and the two add up to 104.8%. The extra 4.8 points are the book's margin, called the vig or juice.
Removing the vig
De-vigging scales both sides back down so they add to 100%. For -150 and +130, the implied chances are 60.0% and 43.5%; divided by their 103.5% total, the fair chances are 58.0% and 42.0%.
Why sharp books
Not every book's prices are equally informative. Sharp books (Pinnacle is the best-known) take large bets from winning players and move their lines to match, so their de-vigged prices are a strong estimate of the true odds. Recreational books shade prices toward what their customers like to bet.
Comparing your book's price with the sharp fair price is the whole idea behind finding an edge: when your book pays more than the fair odds, the bet is worth more than it costs, on average.
Limits worth knowing
- Proportional de-vigging is simple and close enough for most markets; long shots can carry a bit more margin than it assumes.
- Sharp books don't post every market, especially player props. There we fall back to the consensus of many books and label it.
- Fair prices move. A number from this morning may be stale by kickoff, which is why we grade picks on closing-line value.
- A promo doesn't change this: a no-sweat bet or a boost is still only worth taking when the underlying price beats the fair chance.
Try the numbers yourself
Take the vig out of a two-sided price to get the fair chance and the book's hold.
Open the de-vig calculatorSee every price at your books against the fair price
Parity Odds Pro does this math on every bet, prop, and promo, every few minutes.
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