Parlays combine multiple independent bets into a single wager with a larger payout. Standard parlays at most books are negative EV because the payout uses fixed multipliers that undercompensate for true probability.
Example: A 2-leg parlay of two -110 favorites. Each leg implies 52.4% probability, but the no-vig probability is 50%. A fair 2-leg parlay at 50% × 50% = 25% probability should pay +300. Standard books pay +260 — the difference is the vig stacking.
When parlays can be positive EV: 1. Correlated parlays — When two legs are positively correlated (e.g., QB passing yards over + game total over), a parlay pays the same as independent bets but the true probability is higher. Some books allow these; others actively restrict them. 2. Promo parlays — Boosted odds, profit boosts, and insurance offers can flip parlays to +EV. 3. DFS pick'em formats — Platforms like PrizePicks use power-play multipliers that can be +EV for well-calibrated prop pickers.
The parlay EV calculator on sharksnip.com computes exact EV given your estimated win probabilities and the payout offered.