Parlay math: why the margin adds up
A parlay ties several bets together. Every leg must win to get paid. The payout looks big because the chance of winning is small, and the sportsbook's margin is applied to every leg.
How a payout is calculated
Convert each leg to decimal odds and multiply them. A -110 leg is about 1.909 in decimal odds (see American odds). A two-leg parlay of -110 bets pays 1.909 × 1.909 ≈ 3.64, which is +264. A $100 stake returns $364 in total, or $264 in profit.
Fair payout versus real payout
If each leg were a true 50% chance, a fair two-leg parlay would pay 4.00 (+300). The sportsbook pays 3.64 instead. The gap grows with every leg you add.
| Legs (all -110) | Typical payout | Win chance at 50% per leg | Fair payout |
|---|---|---|---|
| 2 | +264 | 25.0% | +300 |
| 3 | +596 | 12.5% | +700 |
| 4 | +1228 | 6.25% | +1500 |
Correlation and same-game parlays
Legs from the same game can be correlated: if a team scores a lot, its player props and the over tend to hit together. Sportsbooks price same-game parlays with that in mind, and the margin on them is often higher than on single bets. Always compare the price of the combo with what the single bets imply.