Comparing Kalshi and Polymarket contracts

Before comparing anything, read both sets of rules at the source. Kalshi publishes contract terms and rules in its own documentation, and Polymarket publishes market resolution rules alongside each market. Anything below is a way of organising that reading; it does not replace it.

Start from the structural differences

Kalshi is a CFTC-regulated designated contract market in the United States, and its contracts are defined by exchange rules with a stated settlement source. Polymarket markets are defined by their published resolution criteria and resolved through the platform's own resolution process. Those are different mechanisms with different failure modes, and a like-for-like comparison has to acknowledge that before it compares prices.

The six things that make two contracts different

Reading a price gap honestly

Suppose one venue quotes 71 cents and another 74 cents on questions with the same headline. Before that three-cent gap means anything, work through the list above. If the settlement sources differ, the contracts are measuring two related but distinct events and the gap is not an inconsistency. If the windows differ, the later contract includes outcomes the earlier one cannot capture. If the size at the quote is small, the gap may not survive contact with an order of any size.

Only once those are ruled out is the residual difference something to think about, and even then it is information about the two venues' participants as much as about the world. A quoted difference is never a risk-free or guaranteed outcome; fees, size, timing and settlement all sit between a quote and a result, and event contracts can lose the full amount at stake.

Practical notes

• Price conventions differ in presentation. Normalise everything to the same unit before you subtract, and write down which convention you normalised from.
• Record both native identifiers in your note. Headlines are edited; identifiers are how you find the same contract again.
• Timestamp both quotes. Two prices read ten minutes apart across a data release are not a comparison.
• Check whether one venue lists several contracts covering parts of the same question. A single contract on one venue often maps to a ladder on the other.
• Keep a short written reason whenever you decide two contracts are not comparable. Those notes are more reusable than the ones where everything matched.

A worked sequence

Pull both contracts. Paste both yes conditions into one document side by side. Highlight every noun and date that differs. If nothing differs, note the settlement sources and confirm they are the same publication. Then, and only then, record the two quotes with timestamps and compute the difference. The whole pass takes a few minutes per pair and it removes most false positives.

Where Riddle fits

Riddle groups candidate contracts across Kalshi, Polymarket and Limitless and puts them on one screen with their venues and identifiers, which is the assembly work in the sequence above. The comparison itself stays with you: grouping is a prompt to review, not a verified equivalence between two contracts.