Why Multi-Leg Contracts Cost More Than Their Legs

Probabilities multiply, spreads and fees repeat on every leg, and correlation bends the rest — why a combo's price never matches its parts.

Published 2026-10-05 · Data as of 2026-10-05 · Market & data intelligence · Educational, not advice.

What a multi-leg contract actually is

A prediction market is an exchange where you contract against other people, not against a house. Every contract has a buyer and a seller; the exchange matches them, takes a fee, and never takes the other side itself. The price is simply where the last buyer and seller agreed — what someone will pay for YES against what someone will accept — and it moves continuously until the outcome is known.

A multi-leg contract bundles several of those outcomes into one position that pays only if every leg resolves YES. Picture three separate questions — a rate decision, an index close, a jobs number — stitched together so the whole thing settles at a dollar only when all three land, and at zero if even one misses. The appeal is obvious: one low-priced contract, one tidy payout. The cost is where intuition quietly breaks.

Probabilities multiply, so the whole is rarer than any part

Start with the clean case, no frictions. Suppose each of two legs carries an implied 50 percent. It is tempting to read the pair as roughly a coin flip, because each piece is. But the combined position pays only when both land, and the chance of both is the two multiplied together — a quarter, not a half.

Add a third 50 percent leg and you are at an eighth. Each leg you add does not subtract from the probability; it multiplies it down. That is why a multi-leg contract carries such a low price: not because the market thinks any single leg is unlikely, but because asking several things to all be true at once is a far narrower event than asking any one of them.

So the price looks cheap, and in dollar terms it is. The thing that is expensive is the probability you are buying. Per unit of real chance, you are paying up — the low sticker hides how far the implied odds have stretched.

Where the extra cost actually hides

Now drop the no-friction assumption, because this is the part the legs genuinely do not advertise.

Every leg has its own spread — the gap between what buyers will pay and what sellers will accept. Cross it once and you give up a little. A multi-leg position makes you cross it on every leg, and those small gives stack. Three legs, three spreads, each nibbling the same position.

Then there are fees. On most venues a fee attaches per contract, and a multi-leg bundle is built from several. So the all-in cost is not the combo price alone — it is the combo price plus the spread on each leg plus the fee on each leg. Sum those and the effective price sits meaningfully above the clean math, even though no single leg looked expensive on its own.

This is the real answer to why multi-leg contracts cost more than their legs suggest. The legs imply a price built from tidy mid-market numbers. What you actually pay is that price after friction has been applied several times over.

Correlation bends the math again

The multiply-them-together rule assumes the legs are independent. Real events rarely are.

If two legs tend to move together — say both ride on the same economic release — then when one lands the other becomes more likely too, and the true joint probability is higher than the naive product. If they move against each other, it is lower. A market that is paying attention prices this in, so the quoted combo will not match what you get by multiplying the legs by hand.

That is the subtle trap. People check a multi-leg price by multiplying the individual legs, see a mismatch, and assume something is off. Often the gap is just correlation and friction doing exactly what they should. Neither is an error, and neither is a signal to act on — it is simply the difference between the mechanics on paper and the mechanics in a live book.

How to think about it from here

A multi-leg contract is not a shortcut to a bigger payout; it is a bundle of narrower odds wrapped in several layers of cost. The low price is the honest part. The friction and the correlation are what the sticker leaves out.

If you want to see how the same legs are priced across venues — and how a bundle stacks up against its parts in one view — Delta Arc's Prediction Markets product brings markets from Kalshi and Polymarket into one place. The next time a combo looks surprisingly cheap, the useful question is not whether to take it, but which of these forces — multiplied odds, stacked friction, or correlation — is doing the pricing.