Prediction market combo & parlay calculator: see what a combo really costs
Enter the market price of each leg and the combo quote. The calculator shows the markup over the legs, your break-even hit rate and your expected value, with an estimated trading fee included.
Legs (example slate, edit freely)
Readout
legs multiplied = P₁ × P₂ × … × Pₙ
This is the fair price if the legs are unrelated. Leave "Your %" blank to use the market price for that leg.
How to check a combo quote
- Enter each leg's market price in cents. A 62¢ price means the market puts that leg at 62%.
- Enter the combo quote you were offered and how many contracts you would buy.
- Read the markup. It is the quote minus the legs multiplied together. A positive markup means you pay extra for the bundle.
- Add your own read in the "Your %" column if you think a leg is more or less likely than its price. The expected value then uses your numbers.
Worked example
Three unrelated legs, say a game, a CPI print and a Fed decision, trade at 62¢, 58¢ and 70¢. Multiplied together they come to 0.62 × 0.58 × 0.70 = 0.252, so a fair combo is about 25.2¢. The quote is 29¢, which is 3.8¢ above fair, a 15% markup.
For 50 contracts, the estimated fee adds 73¢, so the all-in cost is $15.23 for a $50.00 payout. That breaks even only if the combo hits 30.5% of the time. At the market's own 25.2%, the expected value is about −$2.64. The combo needs your read to be meaningfully better than the market's to be worth the price.
Why combos carry a markup
Market makers quote combo prices, and you can only take the quote or pass. Comparing the quote with the legs multiplied shows how much the bundle costs you.
When legs are related
A team winning and that team's quarterback throwing two touchdowns tend to happen together. Legs that happen together push the true price above the legs multiplied, and legs that work against each other push it below.
Fees change the break-even
A fee of a cent or two per contract moves the break-even hit rate by the same number of points. On low-priced combos, that is a large share of the price.
Free guide: The Combo Tax
A short PDF on reading combo quotes, spotting markup and sizing a hedge, with worked examples. Delivered by email.
Questions
How do I know if a combo is priced fairly?
Multiply the prices of the legs as probabilities. Three legs at 62¢, 58¢ and 70¢ multiply to about 25.2¢. A combo quoted at 29¢ costs 3.8¢ more than that, a 15% markup, if the legs are unrelated.
What if the legs are from the same game?
Legs from the same game often move together, so the true combo price is usually higher than the legs multiplied. In that case the markup shown is a ceiling, and the real markup is likely smaller.
What is a break-even hit rate?
It is the share of the time the combo has to hit for you to come out even. A contract that costs 30.5¢ all-in pays $1, so it breaks even if it hits 30.5% of the time.
Is a combo the same as a parlay?
On event-contract exchanges a combo is a single contract that pays only if every leg settles yes. Sportsbooks call the same structure a parlay. The pricing math here applies to both.
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