Kalshi and Polymarket list many of the same events, but they are structurally different venues. Kalshi is a CFTC-designated contract market where US traders post US dollars. Polymarket is an offshore, on-chain exchange collateralized in USDC on Polygon, and it is not available to US persons.
Access is the first fork: a US trading desk chooses between Kalshi and Polymarket US, while a non-US desk can trade Polymarket and, where eligible, Kalshi. After access, the differences that matter are fees, maker economics, and depth.
Side by side
| Kalshi | Polymarket | |
|---|---|---|
| Regulation | CFTC-regulated US exchange | Offshore, on-chain (Polygon) |
| Settlement | US dollars | USDC stablecoin |
| Who can trade | US persons and eligible international traders | Non-US persons only |
| Taker fee | 7% of P × (1 − P), all categories | 3% to 7% by category; geopolitics free |
| Maker fee | 1.75% of P × (1 − P) | None, plus rebates from 20% of taker fees |
| Annual volume | $39.7B (year to Feb 2026), 87% sports | $36.2B (year to Feb 2026), 38% sports |
| Depth at size | 0.11¢ slippage on 50,000 contracts | 0.05¢ slippage, higher top-of-book ask |
| API | REST + WebSocket | CLOB REST + WebSocket |
Taker fees, category by category
Beyond fees: depth and execution
Polymarket undercuts Kalshi's taker schedule in every category except crypto, and its makers trade free while Kalshi's pay 1.75%. But fee schedules are not execution costs. In our live 50,000-contract Fed decision case study, Kalshi had the better displayed ask and the deeper book; Polymarket had the tighter slippage but a higher starting price. The all-in taker costs came out $39,653 on Kalshi and $40,133 on Polymarket, closer than either the quotes or the fee schedules suggested.
The same event often trades on more than one venue at different prices, with different depth at each level. That is the gap smart order routing exists to close: River compares the executable price across venues, splits orders across books, and works them passively where maker economics pay.