Prediction Market Parlay Calculator: How to Compute Combo Odds and Payouts

Prediction market contracts are priced in cents, and that price is the implied probability. A contract at 62 cents is the market saying there is a 62% chance the event happens. That makes parlay math cleaner on a prediction market than at a sportsbook, where you have to unwind American odds and vig before you can see what the book actually thinks.

Here is how to run the numbers on a multi-leg position, how to convert the result into formats you can compare against a sportsbook, and how to figure out whether the payout is actually worth the risk.

The Core Formula

For events that do not influence each other, the combined probability is the product of the individual probabilities.

Combined probability = P1 × P2 × P3 × ... × Pn

Contract prices are already probabilities, so you just divide each by 100 and multiply.

Worked example, three legs:

| Leg | Contract price | Implied probability | |---|---|---| | Team A moneyline | 68 cents | 0.68 | | Game total over | 55 cents | 0.55 | | Player to record 20+ points | 61 cents | 0.61 |

0.68 × 0.55 × 0.61 = 0.228

So the combined probability is 22.8%, and the fair price for the combo is about 23 cents per contract.

Calculating the Payout

A prediction market contract settles at $1.00 if it resolves YES. So your payout multiple is simply:

Payout multiple = 1 / combined probability

Using the 22.8% example: 1 / 0.228 = 4.39x

A $100 stake at a fair price of 23 cents buys about 435 contracts, which pay $435 if every leg hits. Your profit is $335 on a $100 risk.

Here is how the multiple scales as you add legs, assuming every leg is priced at 60 cents:

| Legs | Combined probability | Fair price | Payout multiple | |---|---|---|---| | 2 | 36.0% | 36 cents | 2.78x | | 3 | 21.6% | 22 cents | 4.63x | | 4 | 13.0% | 13 cents | 7.72x | | 5 | 7.8% | 8 cents | 12.86x | | 6 | 4.7% | 5 cents | 21.43x | | 7 | 2.8% | 3 cents | 35.72x |

The payout grows fast. So does the failure rate. At seven legs of 60-cent contracts you are cashing fewer than 3 times in 100 attempts.

Converting to Sportsbook Odds

If you want to compare a combo against a sportsbook parlay, convert the combined probability into the formats books use.

Decimal odds:

Decimal = 1 / probability

American odds (for probabilities under 50%):

American = (100 / probability) - 100

American odds (for probabilities of 50% or more):

American = -1 × (probability × 100) / (1 - probability)

Running our 22.8% example:

• Decimal: 1 / 0.228 = 4.39
• American: (100 / 0.228) - 100 = +339

So that three-leg combo is roughly a +339 parlay in sportsbook terms.

Now go price the same three legs at a sportsbook. If the book offers +290 on the equivalent parlay, the prediction market position is paying meaningfully better for the same risk. If the book offers +360, the book is better. That comparison is the entire reason to do this conversion.

In general, prediction markets tend to compare favorably on multi-leg positions because sportsbook parlay pricing compounds the vig on every leg. A book taking 4.5% on each side of a single game is taking considerably more than that across a four-leg parlay. Prediction market fees are usually smaller and structured differently, though you still need to check them.

Where the Simple Math Breaks Down

The multiplication rule assumes independence. Real sports outcomes often are not independent.

Positive correlation means the legs tend to happen together. "Team A wins" and "Team A's starting quarterback throws for 300 yards" reinforce each other. The true joint probability is higher than the product, so a fair price should be above your calculated number.

Negative correlation means the legs work against each other. "Team A wins" and "game total goes under" can conflict if Team A wins by scoring a lot. The true joint probability is lower than the product, so a fair price should be below your calculation.

On Kalshi, combos are priced through a request for quote rather than posted on an order book, so a market maker is applying their own correlation model when they respond. If the quote comes back well above your multiplication result on a same-game combo, correlation is the likely explanation rather than a bad price.

This is why the calculated number is a reference point, not a target. Use it to understand what you are being asked to pay relative to a naive baseline, then decide whether the adjustment looks reasonable.

Break-Even Hit Rate

A useful sanity check: what fraction of your combos need to cash for you to break even?

Break-even rate = 1 / payout multiple

Which is just the combined probability again. If your combo pays 4.39x, you need to hit 22.8% of the time to break even before fees.

That framing is more useful than it sounds. It reframes "this pays 4.4 to 1" into "I need to be right on all three legs roughly one time in four." If your honest assessment of your edge does not support that, the payout multiple is not the relevant number.

Add fees and the required rate goes up. A combo that needs a 22.8% hit rate at zero cost might need 24% or 25% once trading costs are included, depending on the fee structure and the price range.

Common Mistakes

Treating the payout multiple as the edge. A big multiple means the market thinks the outcome is unlikely. It is not free money. It is correctly priced risk.

Ignoring correlation entirely. Stacking three same-game legs that all depend on the same team blowing out the same opponent is close to a single bet with a parlay price attached.

Forgetting the fee at confirmation. Check the total cost, not the quoted contract price.

Chasing legs to hit a payout target. Adding a fourth leg to turn 4x into 7x does not improve the position. It roughly halves your win probability.

Doing This Faster

Running these numbers by hand for every combination gets old quickly. We built a parlay builder into the market pages on Your Prediction Edge that handles it for you.

On any combo-eligible market you will find a Build a Parlay section listing the other markets in the same collection with their current prices. Select up to seven legs and it calculates the combined probability and estimated payout for whatever stake you enter, updating live as you add or remove legs.

You can browse everything that supports combos on the markets page, and the combo filter stacks with the exchange filter so you can look at Kalshi combos specifically.

The builder uses the independent-events calculation described above, so it gives you the baseline number to carry into the quote request. It is not predicting what a market maker will offer you. It is telling you what the math says before correlation adjustments.

Putting It Together

The workflow that makes sense for most people:

1. Identify the legs you actually have a view on.
2. Multiply the contract prices to get the baseline probability.
3. Convert to American odds if you want to shop it against a sportsbook.
4. Decide which direction correlation should push the price.
5. Compare the quote you receive to that adjusted expectation.
6. Check the break-even hit rate and ask honestly whether your edge supports it.

Most of the value in this exercise comes from step 6. The arithmetic is easy. Being honest about whether you are actually right 23% of the time is the hard part.

For more on reading prediction market prices, see our guide to understanding prediction market odds. If you want the full mechanics of how Kalshi prices combos, read Kalshi parlays explained.