A four-leg same-game parlay carries roughly 40% more hold than a two-leg version built from the same underlying markets — and the jump isn't linear. Going from two legs to three adds more margin than going from three to four, which tells you the pricing damage happens early. Sportsbooks don't hide this; the correlation adjustments baked into SGP pricing are where the real cost sits.
Where the extra hold actually comes from
A straight parlay multiplies the book's margin on each leg. A same-game parlay does something messier: the legs are correlated, so the book can't just multiply independent probabilities. It has to price the joint outcome, and it shades that joint price well beyond the true correlation effect.
Take a typical NFL SGP: quarterback passing yards over, a receiver's receptions over, and the team moneyline. Those outcomes move together. If the QB throws for 300, the receiver probably eats, and the team probably wins. A fair joint price would reflect that overlap. The book prices it as if the legs were closer to independent, then applies a correlation haircut that favors the house.
The result: leg two in an SGP often costs you more in implied margin than leg one, and leg four more than leg three — but the biggest single step is the second leg, not the fourth. By the time you're adding a fourth leg, you're layering on top of an already-thick hold.
A rough number to hold onto
On a standard two-leg SGP with legs priced around -110 each, the effective hold can land near 8–10% once correlation shading is applied. Push to four legs and that figure climbs toward 13–14% on comparable markets. That's the 40% relative increase — not a doubling, but enough that a bettor who wins 52% of the time on two-leg builds needs closer to 55% on four-leg builds to stay level.
Why books lean on SGP limits instead of odds
Most US operators cap SGP payouts well below straight-parlay limits. A $50,000 straight parlay ceiling might come with a $10,000–$25,000 SGP cap, and some books restrict which legs can combine at all. That's a tell. If the pricing were purely fair correlation math, there'd be less need for the limits.
DraftKings, FanDuel, and BetMGM all publish SGP-specific rules buried in their house-rules pages — worth reading before you assume a combination is allowed. A leg that's voided mid-slate can also reprice the whole ticket, sometimes at worse odds than you locked.
What this means for how you build
If you're chasing a longshot, four legs is a worse deal than it looks — you're paying the highest marginal hold for the smallest marginal probability gain. If you're building for entertainment and a modest payout, two or three legs is where the value curve is least brutal.
The open question is whether sportsbooks will keep widening SGP margins as the product matures, or whether competition forces them to publish cleaner correlation pricing. Right now the market is young enough that the hold varies wildly between books on identical combinations — which means shopping the same four legs across three operators can swing your effective price by several percentage points. That's the only real edge most bettors have here, and it requires no prediction at all.