How does a parlay bet work?
A parlay is a single bet that links two or more individual bets together. To win, every leg has to hit. Miss one, and you lose everything.
The appeal is obvious: a small bet, a large potential payout. A $10 two-team parlay at -110/-110 pays $36.45. A 4-team parlay pays about $100 for a $10 stake. Miss any leg and the whole thing is dead.
That's the core mechanics. The math underneath it is worth understanding if you're going to bet them.
How the payout is calculated
Each leg has decimal odds. You multiply them all together, then multiply by your stake.
Converting American odds to decimal: positive odds like +150 → (150/100) + 1 = 2.50. Negative odds like -110 → (100/110) + 1 = 1.909.
Two-team parlay: Team A (-110) × Team B (-110) = 1.909 × 1.909 = 3.645. A $100 bet pays $364.50 total — $264.50 profit.
Three-team parlay at -110 each: 1.909 × 1.909 × 1.909 = 6.96. $100 bet pays $696.
Each additional leg multiplies the payout. It also multiplies the difficulty of winning.
What the sportsbook is actually paying you
Here's where it gets important.
A bet at -110 has an implied probability of 52.4%. That's what the odds say the event will happen.
A true 50/50 bet would be +100 odds (2.0 decimal). The -110 line means the sportsbook is charging you a fee — called the vig or juice — on every bet. That fee is approximately 4.5% per bet at -110.
In a two-leg parlay, that fee compounds. You're not just paying the vig once — you're paying it on each leg, and it multiplies.
Fair payout for a two-team parlay (if both teams are true 50/50): $100 bet should pay $400. Actual -110/-110 parlay payout: $264.50. The difference is the house edge, which is higher on parlays than on straight bets.
What implied probability means for parlays
To win a 4-team parlay where each leg has 50% probability: 0.5 × 0.5 × 0.5 × 0.5 = 6.25% chance of winning.
That means you'd expect to lose roughly 94 out of 100 four-team parlays. A fair payout would be 16x your bet (1/0.0625). Sportsbooks typically pay 10–12x.
The more legs, the bigger the gap between the true probability and the payout offered.
Why sportsbooks offer them
Parlays have a higher house edge than almost any other sports bet. A standard straight bet at -110 carries about 4.5% house edge. A 4-team parlay at -110 per leg carries closer to 30–40% house edge depending on the book.
They offer large payouts that attract bettors. They also rarely get hit. From a business perspective, they're an excellent product.
Same-game parlays
Same-game parlays — where all legs come from the same game — were popularized by FanDuel and have since become standard across major books.
The correlation problem: if you parlay a team to win and their star player to score a touchdown, those outcomes are related. A traditional parlay assumes independence between legs. Same-game parlays should theoretically pay more because correlated outcomes are harder to model. In practice, sportsbooks price them conservatively, capturing even more edge.
The honest assessment
Parlays are negative expected value for the bettor. Every component bet is already negative expected value (because of the vig), and combining them makes it worse.
That doesn't mean you shouldn't bet them. A $10 parlay with a $800 payout is entertainment with a defined downside. That's a legitimate use. Treating parlays as a reliable income strategy is where people get into trouble.
The math doesn't change regardless of how confident you feel about a particular game.
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