Two linked coin flips that land together 30% of the time are worth +233, not +300.
01 · Independent legs
A normal parlay multiplies the legs
In a parlay across different games, each leg has nothing to do with the others, so the chance that all of them land is the product of each chance. Two fair coin flips land together 25% of the time, and the fair price for that is +300.
Books price ordinary parlays the same way, using the prices with the cut still in. Two legs at −110 multiply to 3.645 in decimal odds, or +264, which implies 27.4%. Each leg's cut compounds, which is why parlays are expensive by default.
Inside one game, outcomes share a cause. A fast pace lifts both teams' points. A blowout cuts the starters' minutes on both sides. A quarterback's yards and his receivers' yards are partly the same yards. When two legs tend to land together, the chance that both land is higher than the product, and the fair price is shorter.
Worked example · Quarterback over and his top receiver over
- Each leg, fair
- 50%
- Both land, if unrelated
- 25% · +300
- Both land, if linked
- 30% · +233
- Book's same-game price
- +220
- Book's price implies
- 31.3%
If the true joint chance is 30%, the fair price is +233. A book offering +220 implies 31.3%, so it has priced the link and then some: that bet is below fair. A book offering +264 (the two legs simply multiplied) would be paying above fair for the same linked pair.
The 30% here is an illustration. The real link between two legs has to be measured from games, and it varies by team, by role and by how the game is expected to go. That measurement is what our correlation desk does.
03 · Negative links
Some legs work against each other
Correlation can run the other way. A running back's rushing yards and his quarterback's passing yards can pull against each other, because a team that runs well often throws less. Stacking two negatively linked overs makes the parlay less likely than the product, and the multiplied price flatters it.
Before you bet
What this means for your next bet
- Ask whether your legs share a cause. If they do, the product is the wrong chance.
- Estimate the joint chance, then the fair price, before you look at the book's number.
- Compare the book's same-game price with your fair price, not with the multiplied legs.
- Keep parlays small. Every extra leg adds cut and variance.
Questions3 questions
What is correlation in a same-game parlay?
Correlation means two legs tend to land (or miss) together because they share a cause, like a quarterback's passing yards and his receiver's receiving yards. It makes the chance of both landing different from the product of their separate chances.
Do sportsbooks price correlation into same-game parlays?
Most do. They adjust the combined price for the link between legs and usually add a larger margin than on single bets. Whether the final price is above or below fair depends on how strong the real link is.
Are same-game parlays a good bet?
Usually not at the default price, because the cut is larger than on single bets. They can be when you have measured a link the book has underpriced. Size them small either way.
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