How parlay odds work: why every leg multiplies
How do parlay odds work?
A parlay only cashes if every leg hits, so you multiply each leg's chance. Two legs that each hit 70% of the time hit together about 49% of the time, three about 34%, four about 24%. The payout is built the same way: each leg's decimal odds multiply. Assumes the legs don't affect each other.
The rule: multiply
Each leg has a chance of hitting. A parlay needs all of them, so its chance is those numbers multiplied together. That is why a ticket full of likely legs can still be unlikely.
| Each leg hits | 2 legs | 3 legs | 4 legs | 5 legs |
|---|---|---|---|---|
| 60% | 36% | 22% | 13% | 8% |
| 70% | 49% | 34% | 24% | 17% |
| 80% | 64% | 51% | 41% | 33% |
| 90% | 81% | 73% | 66% | 59% |
Turning odds into a chance
American odds convert to an implied chance. A favorite at -150 implies 60%. An underdog at +150 implies 40%. A -110 line implies 52%, a bit over a coin flip because the price includes the book's margin.
How the payout is built
Books multiply each leg's decimal odds. Two -110 legs pay about +264. If each leg were a true 50/50, a fair price for both would be +300. The gap is the margin, and it compounds with every leg you add: three -110 legs pay about +596 against a fair +700.
Two exceptions
- Correlated legs. If one leg makes another more or less likely, simple multiplication is off. See correlation traps.
- Same-game parlays. Books price them with correlation built in, so the payout usually is not the multiplied odds of the legs.