The short answer
Both quote a probability, and both quote it the same way: as the price of something that pays one unit if an event happens and nothing if it does not. A contract at 23 cents is a 23 percent probability in either venue.
The differences are structural, and there are five of them worth knowing before putting the two numbers side by side.
- What can be asked. An option chain answers questions about the level of one underlying at one of its listed expirations, and nothing else. A prediction market can list any question somebody wrote settlement rules for.
- How the number is produced. The option number is derived from prices nobody quoted as probabilities. The event contract price is quoted directly.
- Granularity. One chain produces a probability at every listed strike simultaneously. One event contract produces one.
- What it settles against. An index option settles on an exchange-calculated value with a published rule. An event contract settles on whatever the resolution source in its rules says.
- Whose risk premium is inside it. Different populations hold the two instruments for different reasons, so the gap between the price and any honest frequency estimate is built differently.
The derivation difference
Nobody on an options exchange quotes a probability. They quote calls and puts, and the probability is recovered from the slope of the call price across adjacent strikes. Options implied probability works through that extraction and the arithmetic behind it.
That matters for two practical reasons. The probability can be wrong in ways the quoted price cannot: if the two strikes bracketing your level are far apart, the answer is an average over the whole interval between them, and if the quotes are stale or wide, the subtraction is measuring the spread. A directly quoted event contract has its own failure modes, mostly thin or one-sided books, but the arithmetic step is not one of them.
The second reason is coverage. Because the number is derived rather than listed, every strike on the chain yields one. On 2026-09-22, the SPX chain expiring 2026-10-16 produced a settlement probability at every level across a band about five percent either side of spot, eleven readings out of a single chain, ranging from a 95 percent chance of settling above 7,390 down to about a 2 percent chance of settling above 8,170. No venue lists eleven separate contracts on the same index for the same date.
The coverage difference, in the other direction
The chain is silent on everything that is not the level of its underlying. An election, a policy decision, a court ruling, a data release beating a threshold: an option chain cannot price any of those directly, however much they move prices. Event contract venues exist precisely to list them.
Where the two overlap is narrow: a question of the form "will this index be above this level on this date" can exist in both places. That overlap is the only place a comparison is meaningful at all, and even there the list above applies.
The settlement difference
An index option settles on a value the exchange calculates by a rule published in the contract specifications. There is essentially no ambiguity about what number settles it, and disagreements are about the level, never about the definition.
An event contract settles on a resolution source named in its own rules. That introduces a category of risk with no analogue in a cash-settled index option: the event can happen in the ordinary sense while the contract resolves the other way, or the resolution source can be delayed, revised or contested. A price quoted at 90 cents in that venue is pricing both the event and the resolution.
The premium difference
Neither number is a forecast. Both are prices, and a price includes compensation for bearing risk.
For index options the shape of that premium is documented and one-directional. Portfolio managers buy downside protection because the loss it insures against is correlated with everything else they own, so the priced probability of a large decline sits above the rate at which declines of that size have happened. The implied probability explainer covers that gap and why it means "protection against a five percent fall costs six cents on the dollar" is the correct reading rather than "there is a six percent chance."
An event contract on an unrelated question has no such structural hedger. Its price sits away from a frequency estimate for different reasons: fees, the capital locked against the position until resolution, and whoever happens to be in the book. That makes the two premiums different in kind, not just in size, which is the reason a gap between an options-derived probability and an event contract price is not automatically an arbitrage or a disagreement about the world.
What we publish, and what we do not
The implied odds page reads the settlement probabilities off the delayed Cboe chain for SPX, SPY and QQQ, publishes the method and the conditions under which it refuses to publish a number at all, and dates every reading with the chain it came from. It carries no event contract prices, and nothing on this site compares a live options-derived probability with a live event contract price.
The general point survives the absence. A quoted probability is a price wherever it appears, and the first question about any of them is what the price is compensating for.
Educational content, not financial advice. See our risk disclosure.