Why parlays are usually -EV

Vig compounds. A single -110 NFL spread carries about 4.76% vig. Two -110 legs in a parlay compound that into roughly 9.3% combined vig; three legs go to about 13.6%. Even if each leg is a true 50/50, the book's "combined" price gives you a 2.625x multiplier (6.97 decimal) instead of the true 8.0x that 12.5% probability would warrant. You're paying 14% off the top.

Parlays are profitable in three narrow scenarios: (1) every leg is independently +EV beyond the per-leg vig, (2) the legs are positively correlated and the book hasn't priced the correlation in, or (3) you're betting a same-game parlay where the book's correlation pricing has slipped. Most rec-book parlays satisfy none of these.

Recommended workflow

Use the No Vig Calculator to get a fair probability for each leg from the book's odds.
Adjust each leg's "Your true prob" if your own model disagrees with the market — even 1 point of disagreement compounds across legs.
Read the per-leg edge readout. If any leg is meaningfully -EV (worse than -1%), drop it or reprice it before parlay-ing.
If the parlay EV is +EV, size the bet with the Kelly Calculator using the parlay probability and combined decimal odds.

FAQ

Are parlays profitable? +

In expectation, almost never. Each leg of a parlay carries its own vig, and books multiply those vigs together for the combined price. A 3-leg parlay of -110 sides has an effective hold of roughly 13.6% — almost three times the per-leg vig. The math gets worse with more legs. Parlays are profitable in two narrow cases: when individual legs are independently +EV (rare), or when the legs are positively correlated and the book has not priced the correlation in.

What does "correlated parlay" mean? +

Two legs are correlated when the outcome of one shifts the probability of the other. Classic example: betting the over on team total points and the over on game total — if team A scores more, the game total is more likely to also go over. Books reject many same-game parlays for this reason, or price the multiplier lower than the product of leg odds. When you flag the correlation checkbox in this calculator, the EV math is unchanged (still assumes independence) but a warning appears: positive correlation makes your true parlay probability higher than the naive product, which means the book's "correlated parlay" pricing is sometimes a real edge.

How is parlay EV calculated? +

For independent legs: parlay_prob = Π(leg_prob_i); payout_multiplier = Π(decimal_odds_i); win_payout = stake × payout_multiplier; EV = parlay_prob × win_payout − (1 − parlay_prob) × stake. The leg edges shown in the table tell you whether each individual leg is +EV at the offered odds; even one −EV leg can drag a parlay's combined EV negative.

Why does the parlay show -EV even when every leg is +EV? +

Compounded vig. If every leg is 2% +EV at -110, the legs are still about 50% true probability with a 52.38% implied. Multiply three independent legs of 50% true (parlay prob ≈ 12.5%) against the parlay payout multiplier (decimal 6.96, $696 win on $100) — EV is +$2.30, or +2.3%. With a 1% per-leg edge on the same -110, parlay EV flips negative. Parlays require larger per-leg edges to overcome the compounded vig.

Should I round-robin instead of parlay? +

Round-robins (a set of smaller parlays from a pool of legs) reduce variance but not vig — the round-robin's EV is the average of the constituent parlay EVs, weighted by stake. If each constituent is -EV, the round-robin is -EV. Use round-robins only when individual parlays are +EV and you want to smooth variance.

Parlay EV Calculator