A useful Polymarket-versus-Kalshi comparison starts with which Polymarket product and which sports contract. Brand-level claims such as “Polymarket always has deeper books,” “Kalshi is US-only” or “the exchange has no fees” do not select the better execution for a particular order.
Resolve the product and access question
The CFTC record identifies QCX d/b/a Polymarket US as a designated contract market. Its separate US documentation describes the US-dollar product. International uses a different product and restriction policy; see the US/International explanation.
Kalshi’s individual account guidance describes domestic and eligible international access. Account eligibility and restrictions on specific contracts still need their own checks. Neither regulatory status nor website access guarantees that every person can use every sports market.
Match the settlement, then compare the price
| Check | What to compare |
|---|---|
| Event | Same game, teams, date and outcome |
| Settlement | Regulation time versus overtime, postponements, cancellations and source |
| Quote | Bid for an exit; ask for a purchase; not a last trade mixed with a midpoint |
| Size | Quantity actually available at the intended price and deeper levels |
| Cost | The applicable fee and weighted fill price, including partial/non-fill cases |
| Time | Quote age and the timing of any related score or news input |
Use Kalshi’s published fees, Polymarket US fees or the relevant International fee rules for the actual market. A single fixed cent or percentage adjustment does not represent every product and order type.
In a hypothetical $1 contract at 58c, the gross break-even rate is 58%. A model estimate of 65% gives a conditional 7c expected margin before costs; it does not validate the true chance or prove that either venue is mispriced.
What ZenHodl’s historical comparison can establish
Our MLB depth report describes a short June 2026 sampled capture with observation and level limits. The lead-lag study and cross-venue study also have narrow population and execution limits. Their findings are not an exchange-wide liquidity ranking or a current executable arbitrage result.
A documented archive can help answer a defined historical question. Its row count does not certify complete season coverage. Inspect the sample schemas and product’s observed bounds before assuming that an advertised cutoff is every market’s first or last observation.
This October 8 rewrite removes unsupported volume/growth rankings, zero-fee claims, broad legal clearance, hypothetical returns presented as live advantages and claims that a calibrated probability source guarantees profitable venue selection.