How BetterSlip's AI quantifies the vig on every bet
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An AI betting tool calculates the vig, also called hold, by converting every side of a market to an implied probability and adding them together. Whatever the total sits above 100% is the vig, the price a sportsbook charges you for taking a bet at all, and it's paid whether the bet wins or loses. BetterSlip's AI runs that calculation continuously across every connected sportsbook so the vig isn't a hidden number buried in the odds, it's a figure you can see and compare before you bet. That number matters because it isn't fixed. It moves by book, by market type, and by how many outcomes a bet touches, and knowing where it's highest changes both which bets are worth making and which sportsbook is worth making them at.
What is vig, in plain terms?
Vig is the sportsbook's fee for offering a market at all, built directly into the price rather than charged separately. A perfectly fair coin-flip market, one with no house edge, would price both sides at plus-100, since either side has an exactly 50% chance and a $100 win and a $100 loss offset evenly. Real markets don't do that. A standard point spread priced at -110 on both sides implies 52.38% on each, which adds up to 104.76%, not 100%. That extra 4.76% is the vig on that market, and it's collected from the losing side of every bet placed, regardless of who wins. You never see a separate line item for it on a bet slip. It's baked directly into the number.
How much vig does BetterSlip's AI find across different bet types?
Vig isn't a single figure. It varies by how a market is structured, and the pattern holds up consistently once you look across enough of them.
Standard mainlines, point spreads, totals, and moneylines close to even money, typically carry the tightest margin, generally landing somewhere around 4% to 5% depending on the book and how close the number is to a true coin flip. Player props usually run wider than mainlines, since a single prop draws less action and less competitive pressure between sportsbooks than a game's own spread does, and BetterSlip's own player props coverage has walked through a specific prop example carrying close to 7% built in. Alternate lines, where a book is pricing a shifted number rather than its main line, tend to run wider still, since there's a smaller, thinner market on each individual alternate number. Futures markets carry the widest hold of any standard market type, often well into the double digits once every outcome across a multi-team field is added up, because a book can shade a dozen or more longshot prices at once without any single number looking obviously out of line. Same-game parlays sit above all of them. A packaged SGP price folds a book's own correlation adjustment into a single number with no public formula behind it, and that opacity is exactly why an SGP typically carries the highest hold of any bet type a standard sportsbook menu offers.
Put together, that's a rough ladder from tightest to widest: mainlines, then player props, then futures, then same-game parlays, each step reflecting a market with less competitive pressure and less transparency than the one before it. None of that means every prop or every future is a bad bet. It means the price has more built-in cost to clear before a bet is actually worth taking, and that cost is exactly what a devig calculation, covered in full in BetterSlip's companion post on how the AI devigs odds, is built to measure.
Worked example: the same bet priced at three books
Vig also varies within a single bet type, book to book, on the exact same game. Take a spread's favorite side priced at three different sportsbooks the same afternoon.
Book A: favorite -108, underdog -106
- Favorite implied: 108 ÷ 208 = 51.92%.
- Underdog implied: 106 ÷ 206 = 51.46%.
- Total: 51.92% + 51.46% = 103.38%. Vig: 3.38%.
Book B: favorite -122, underdog -102
- Favorite implied: 122 ÷ 222 = 54.95%.
- Underdog implied: 102 ÷ 202 = 50.50%.
- Total: 54.95% + 50.50% = 105.45%. Vig: 5.45%.
Book C: favorite -115, underdog -118
- Favorite implied: 115 ÷ 215 = 53.49%.
- Underdog implied: 118 ÷ 218 = 54.13%.
- Total: 53.49% + 54.13% = 107.62%. Vig: 7.62%.
Same game, same two sides, and a gap of more than four full percentage points in vig between the cheapest and most expensive book to bet through. On a $100 bet, Book A's 3.38% hold and Book C's 7.62% hold aren't just abstract numbers, they translate directly into how much of your action is going toward the book's margin rather than into your own edge, before a single game has even been played. This is illustrative math to show the method, not a live quote, but the spread between books shown here is an ordinary one on a real slate, not an exaggerated example.
What does knowing the vig change about which bets to make?
Once vig is visible rather than hidden, it becomes a filter, not just a fact. A player prop that looks favorable against the posted number can shrink or disappear once the wider margin typical of props is stripped back out, because that margin is a bigger hurdle for a real edge to clear than a mainline's margin is. A futures bet on a long-priced team carries so much built-in hold that even a modestly favorable line can still be pricing that outcome worse than it should. Knowing the rough vig on a bet type before you bet it means judging the price against a realistic bar instead of assuming every posted number is close to fair.
This is also where BetterSlip's Low Hold Finder does its specific job: it scans for pairings across markets and books where the combined vig sits as close to zero as possible, which is a different use case from finding a single mispriced side, but draws on exactly the same underlying calculation.
What does knowing the vig change about which sportsbook to use?
The three-book example above is the practical version of this question. If the same game is available at 3.38% hold at one book and 7.62% at another, betting through the cheaper book isn't a marginal preference, it's a direct reduction in the fee you're paying to place the exact same bet. That gap compounds across a full slate of games and a full season of betting, in a way that a single afternoon's numbers don't make obvious on their own.
BetterSlip's Best Odds Finder is built around exactly this comparison, pulling the same market across every connected sportsbook and surfacing whichever one is currently charging the least to take that side. It doesn't require running the vig arithmetic yourself for every game on a card. It runs the comparison continuously and shows you where the current gap actually is.
Track the vig on your next bet with BetterSlip
Open the Positive EV Finder to see a specific market's devigged fair price and which book is offering value against it, or the Best Odds Finder to compare the raw price on a side across every connected sportsbook. Ask BetterSlip's AI assistant at betterslip.com/chat directly what the vig looks like on tonight's game and it pulls the live comparison rather than a generic estimate. Odds comparison across 25+ sportsbooks is free with no account needed. Getting the two vig-focused tools above, plus the rest of BetterSlip's 90+ tracked sportsbooks, means stepping up to the $79-a-month Elite plan, which comes with a 3-day trial to test the comparison before paying for it. None of this changes whether a given bet wins, and it's only usable where sports betting is legal in your state or country.
What tracking the vig doesn't do
Quantifying the vig tells you what a bet costs relative to a fair price. It doesn't tell you whether any specific bet is going to win, and a low-vig bet can still lose just as easily as a high-vig one. It also can't see inside a same-game parlay's proprietary correlation pricing the way it can devig a plain two-sided market, so an SGP's true hold is harder to pin down precisely than a standard spread's, even though it's reliably the highest of the group. And a vig figure calculated right now can move within minutes as prices shift, so treat any specific percentage as a snapshot rather than a fixed number that holds steady for the rest of the day, and glance at it again shortly before you actually place the bet.
Frequently asked questions
How does an AI betting tool calculate the vig on a market? It converts each side of a market to an implied probability using the standard American-odds formulas, then adds those probabilities together. Whatever the total sits above 100% is the vig, the sportsbook's built-in margin on that specific market.
Why does the vig matter if I'm just trying to place a bet? Because it's a real cost baked into every price, paid regardless of whether the bet wins or loses. A bet that looks appealing on the posted number can turn out to be poor value once a wide vig on that market type is priced in, and comparing the vig across books on the same bet can mean paying meaningfully less to make the identical wager.
Do all bet types carry roughly the same vig? No. Standard mainlines usually run the tightest, around 4% to 5%. Player props typically run wider, futures markets wider still, often well into double digits across a full field, and same-game parlays carry the highest and least transparent margin of the group, since their pricing folds in a book's own correlation adjustment.
Can two sportsbooks charge different vig on the exact same bet? Yes, routinely. The worked example above shows three books pricing the identical matchup with vig ranging from 3.38% to 7.62%, a real and ordinary gap rather than an unusual one, which is exactly why comparing the same bet across books before placing it is worth the extra step.
Does a lower vig mean a bet is more likely to win? No. Vig measures the cost built into a price, not the probability that a specific outcome happens. A low-vig bet and a high-vig bet on the same outcome carry the same real-world result either way, the vig only changes how much of your stake is going toward the book's margin rather than your own potential edge.
Sports betting is 21+ and legal only in certain states and countries. Bet within a bankroll you can afford to lose, and use the vig figures above as a way to compare prices, not as a guarantee about how any bet turns out.