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Are parlays ever +EV?
Arbs research desk · Updated 2026-11-01 · Reviewed 2026-11-01 · 2 min read
The short answer: A parlay multiplies the odds of its legs, and with them the book’s margin. Three −110 legs carry about three times the vig of one. Parlays are +EV only when the legs are +EV on their own, or when the price ignores how the legs move together.
The math of a parlay
A parlay pays the product of its legs’ decimal odds. If the legs are independent, its true chance is the product of their probabilities:
D = d₁ × d₂ × …; P = p₁ × p₂ × …; EV = D × P − 1
That means a parlay’s EV is every leg’s EV compounded:
1 + parlay EV = (1 + EV₁) × (1 + EV₂) × …
Compounding margin
Three coin flips at −110 pay +596. Their fair price is +700. The gap is the compounded vig, and it grows with every leg:
| Legs | Parlay odds | Fair odds | EV |
|---|---|---|---|
| 1 | −110 | +100 | −4.5% |
| 2 | +264 | +300 | −8.9% |
| 3 | +596 | +700 | −13.0% |
| 4 | +1228 | +1500 | −17.0% |
| 5 | +2436 | +3100 | −20.8% |
Case one: +EV legs
If each leg is underpriced, the parlay is too, and the edge compounds. Three legs at +3% each make a parlay worth 1.03³ − 1 = +9.3%.
Case two: correlation
Legs from one game are linked. A team covering and its quarterback passing for a lot of yards tend to happen together. For two yes/no legs with correlation ρ, the chance both hit is:
P(A and B) = p_A × p_B + ρ × √(p_A(1 − p_A) × p_B(1 − p_B))
Worked example: Two 50% legs priced as independent at +264
- Independent: 0.50 × 0.50 = 25%, EV = 3.645 × 0.25 − 1 = −8.9%
- With ρ = 0.2: 0.25 + 0.2 × 0.25 = 30%
- EV = 3.645 × 0.30 − 1
+9.3%. Correlation alone turned a bad parlay into a good one.
Same-game parlay pricing tries to adjust for this, usually with extra margin on top. The Arbs parlay builder simulates correlated legs together and shows the true hit rate and the odds you need to beat. The parlay calculator has a correlation slider.
Try it: Parlay calculator
Frequently asked questions
Why do sportsbooks push parlays?
Because their margin compounds with each leg, parlays earn books more per dollar than single bets.
Are Polymarket parlays better?
Polymarket combos are priced by quotes from market makers. Compare the quote with the product of the legs’ fair probabilities to see the margin.
How many legs are too many?
Every leg adds margin and estimation error. Two- and three-leg parlays of legs you think are +EV are easier to justify than long ones.