Prop parlay builder
Add legs from the live board and it prices the whole slip — the offered payout, the fair payout with the hold stripped out of every leg, and exactly what the parlay is costing you.
What a parlay really costs
Books love parlays because the hold compounds. Two legs at 4.5% hold each is not 4.5% — it is closer to 9%, and a six-leg slip can be carrying a quarter of your stake before the first snap. This tool shows you that number instead of hiding it.
The fair payout
Every leg's price is de-vigged first, then multiplied together. That gives the payout the slip would return if the book took no fee at all. The difference between that and what you are actually offered is the true cost of the parlay, expressed as one number.
Correlation is not modelled here, on purpose
A quarterback's passing yards and his top receiver's receiving yards are not independent events, and a same-game slip built out of correlated legs is priced differently by the book for exactly that reason. This builder prices legs as independent, which is the honest floor. Treat a correlated slip's fair number as approximate and lean on the tape for each leg.
Build from the gap board if you want legs that already pay above fair, and shop every one of them on the ladder before you take the slip.