Parlay Builder
Stack up to 8 Polymarket or Kalshi positions into one combined bet. See the combined probability, payout multiple, and expected value across the whole parlay.
Combined probability = product of individual probabilities. Combined payout = product of individual payout multiples. Combined EV = combined probability × payout minus stake. Assumes legs are independent.
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Parlay FAQ
- What is a prediction market parlay?
- A parlay is a combined bet on multiple independent events resolving in your favor. If you bet 3 markets at 50% each, the combined probability is 0.5 × 0.5 × 0.5 = 12.5%, but the payout multiplies. Parlays turn small edges on individual markets into large potential returns, at the cost of much higher variance.
- How do I use this parlay builder for Polymarket?
- Add up to 8 positions. For each, enter the market price and your estimated probability. The builder computes the combined YES probability, the combined payout multiple, and the total expected value of the parlay. Green EV means the parlay is a good bet; red means skip it.
- Are these markets assumed to be independent?
- The default calculation assumes independence. In reality, many prediction markets are correlated (e.g. 'Trump wins' and 'Republicans take Senate' are not independent). Treat parlays on correlated markets as upper-bound probability estimates, not exact.
- What is the biggest mistake with parlays?
- Sizing too big. Because parlay probabilities multiply down, a 3-leg parlay often has resolve probability under 20%. Even with positive EV, you will lose 4 out of 5 attempts. Size with Kelly assuming the parlay probability, not the individual leg probability, or use half-Kelly to reduce variance.
- Can a parlay ever have positive expected value?
- Yes, but only if every leg individually has positive EV. The EV of a parlay is the product of EV multipliers. If any one leg has negative expected value, the whole parlay has negative EV. Avoid the casino-style 'parlay cards' where houses pad the lines on each leg.
Worked example
Three independent markets, each priced at 40¢ YES, where you estimate true probability at 50%.
Combined resolve probability: 0.5 × 0.5 × 0.5 = 12.5%.
Combined payout multiple: (1/0.40)³ = 15.625x.
EV per dollar staked: 0.125 × 15.625 - 1 = 0.953, or +95.3% expected return.
Caveat: you win ~12.5% of the time. Eight attempts to expect one win. Size small.