Parlays are fun: small stake, big payout. They are also where sportsbooks make a huge share of their profit. The reason is simple multiplication. Here is the math, and the narrow cases where parlays make sense.
How parlay odds work
A parlay's decimal odds are the product of its legs' decimal odds. Three legs at −110 (1.909 each):
All legs must win. (How parlay odds are calculated · Parlay calculator.)
The margin compounds
If each leg is a true 50/50, fair odds for each are +100 (2.00). The fair three-leg parlay pays 2 × 2 × 2 = 8.00 (+700). The book pays 6.96 (+596).
| Legs (−110 each) | Book pays | Fair pays | Your expected loss |
|---|---|---|---|
| 1 | +91 | +100 | −4.5% |
| 2 | +264 | +300 | −8.9% |
| 3 | +596 | +700 | −13.0% |
| 4 | +1228 | +1500 | −17.0% |
| 6 | +4741 | +6300 | −24.4% |
| 10 | +64,208 | +102,300 | −37.2% |
Each leg's margin multiplies through. A 6-leg parlay at standard prices gives up roughly a quarter of every dollar bet, on average.
Why people still love them
- Small stake, life-changing payout
- One bet to follow instead of six
- Wins feel huge and memorable; losses feel small and forgettable
Nothing wrong with a small parlay for fun, as long as you know you are paying for entertainment.
When parlays can be +EV
1. Every leg is +EV
If each leg has a real edge, the parlay compounds the edges instead of the margin. Three legs each at +3% edge → about +9.3% as a parlay. The catch: variance rises dramatically, and the edges must be real.
2. Correlated legs that the book underprices
If two outcomes tend to happen together (a team's moneyline and its QB's passing over), the true parlay probability is higher than the product. Most books now price correlation in same-game parlays, usually with extra margin, but mistakes happen. (Same-game parlay correlation.)
3. Promotions
Parlay boosts, insurance and odds boosts can make a parlay +EV even when the legs are not. (Odds boosts.)
4. Teasers in specific spots
Six-point NFL teasers crossing 3 and 7 have historically been one of the few structurally favorable parlay types. (Teaser betting.)
Round robins
A round robin splits your picks into many smaller parlays; each one still carries parlay margin. (Round robin bets explained.)
Parlays and bankroll
Even +EV parlays have enormous variance. A 4-leg parlay with a positive edge can lose 20+ times in a row. Size parlays as a small fraction of a normal unit. (Bankroll management.)
Frequently asked questions
Why are parlays bad bets?
Because the sportsbook's margin multiplies with each leg, so the longer the parlay, the bigger the share of your stake the book expects to keep.
Can parlays ever be +EV?
Yes, when each leg is +EV, when correlated legs are underpriced, or when a promotion adds enough value.
What is the best number of legs in a parlay?
From a value standpoint, fewer is better. Two or three +EV legs keep variance manageable; long parlays mostly add margin.