Every sportsbook makes money by embedding a commission — the vig, or juice — directly into the odds. A standard spread or total is priced at -110, meaning you risk $110 to win $100. That gap between what you'd get at true 50/50 odds and what you actually get paid is the house edge on a single bet. Now string two or more of those legs together, and something uncomfortable happens: the vig compounds. Each leg's built-in edge multiplies against the others, so a four-leg parlay doesn't carry four times the single-bet edge — it carries significantly more. Understanding that math is the foundation of understanding why parlays are high-risk wagers before a single game tips off.
To understand how legs combine in the first place, read How NBA Parlays Work — Legs, Multiplied Odds, and Why One Loss Kills the Ticket. Once you know the structure, the edge calculation makes more sense.
How does the vig actually compound across parlay legs?
Here's the mechanic. At -110, a sportsbook is pricing each side of a market at an implied probability of 52.38% — which adds up to 104.76%, not 100%. That 4.76% overage is the vig. When you build a parlay, you convert each leg to its decimal odds and multiply them. But because those decimal figures already have the vig baked in, you're multiplying inflated implied probabilities together. The true fair-odds payout on a two-leg -110 parlay would be around +300. Standard books pay roughly +264. That gap widens with each leg added. By a four- or five-leg ticket the difference between fair value and what you're actually paid becomes significant. Accepting -120 instead of -110 on even one leg accelerates the damage — consistently accepting worse lines erodes expected value significantly over time.
Why are same-game parlays the most expensive bet type on the board?
Same-game parlays carry some of the highest house edges of any bet type available at a sportsbook. The reason is layered. First, the standard vig compounding described above applies. Second, sportsbooks add an extra margin when legs come from the same game because correlated outcomes — say, a team's moneyline and a player prop for a player on that team — reduce the book's natural risk offset. To compensate, the sportsbook shades the odds further. Third, SGP markets lean heavily on player props, and vig on player props can vary widely across sportsbooks. A bettor who doesn't line-shop can quietly bleed expected value without realizing it. For a full breakdown of SGP rules and correlation costs, see the NBA Same-Game Parlay Guide — SGP Rules, Correlated Picks, and High House Edge.
Is the industry seeing more parlay volume for a reason?
Yes, and the numbers are telling. Parlay volume accounted for approximately 27% of all money wagered in IL, NJ, and CO over the first ten months of 2023, up from 22% in 2021. That growth reflects heavy sportsbook marketing of parlay products — not evidence that recreational bettors are beating them. The sportsbook keeps the spread between fair odds and actual payout on every ticket. More volume at higher margins is a straightforward business outcome. That context doesn't make parlays off-limits, but it's worth knowing before you build a five-legger expecting lottery-style value.
What does this cost per ticket, in real terms?
Run the numbers before you bet. A two-leg parlay with both sides at -110 pays around +264 on most books. The mathematically fair payout at true 50/50 probability would be closer to +300. On a $50 wager that gap is roughly $18 in theoretical value surrendered on a single ticket. Scale that to a five-leg SGP with player props priced at -120 or worse on several legs and the implied cost per ticket grows substantially. Use the NBA Parlay Payout Calculator — Figure Your Return Before You Bet to model your exact ticket before placing it. Seeing the fair-value comparison alongside the posted payout is one of the cleaner ways to understand what the house edge actually looks like in dollar terms.
Does a push on one leg affect the edge calculation?
A push reduces the number of active legs, which does lower the total compounded vig — but you're also collecting on fewer legs than you originally planned. Most books drop the pushed leg and recalculate at the reduced-leg payout. Whether that's better or worse than a loss depends on the ticket. Get the full rules explained at What Happens When an NBA Parlay Leg Pushes — Rules, Adjusted Odds, and What You Collect.
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