For a US trading desk, Kalshi and Polymarket US are the two regulated ways to trade event contracts at size. Both are CFTC-licensed and dollar-settled, and they increasingly list the same events, which makes the comparison unusually direct: same outcome, two books, two fee schedules.
Side by side
| Kalshi | Polymarket US | |
|---|---|---|
| Regulation | CFTC-regulated US exchange | CFTC-regulated via the QCEX acquisition |
| Settlement | US dollars | US dollars |
| Who can trade | US persons and eligible international traders | US persons |
| Taker fee | 7% of P × (1 − P), all categories | 4% to 7% by category; geopolitics free |
| Maker fee | 1.75% of P × (1 − P) | None |
| Rebates | None | Weekly rebates above $250k monthly taker volume |
| Track record | Live since 2021, deepest US books | Relaunched December 2025, waitlist dropped May 2026 |
| Depth at size | 0.11¢ slippage on 50,000 contracts | 3.62¢ slippage on the same order |
Taker fees, category by category
Beyond fees: depth and execution
On paper, Polymarket US is cheaper in every category but crypto, and it never charges makers. In practice, our live 50,000-contract case study showed why the fee schedule alone misleads: Polymarket US displayed an ask just one cent above Kalshi's, but filling the full order there would have walked the book 3.62¢, making it the most expensive route all-in at $41,741 versus Kalshi's $39,653. Until the young books deepen, size belongs on Kalshi and price improvement comes from working orders, not from the schedule.
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.