BANGER
2026-06-01 · 6 min read

Polymarket vs Kalshi: Differences for Traders

Polymarket and Kalshi are the two largest prediction-market venues, and they are converging on the surface while staying very different underneath. As of 2026 both run CFTC-regulated exchanges that US persons can legally trade on, but the regulatory structure, settlement rails, fee math, market mix, and API surface diverge in ways that matter once you are sizing positions or writing a bot. Here is the honest breakdown.

US legality and regulation

Kalshi has held a CFTC Designated Contract Market (DCM) license since 2021. A DCM is the same registration class as a conventional futures exchange, so Kalshi has been legally available to US persons in all 50 states for years. It is the cleanest regulatory posture in the space.

Polymarket spent four years geofenced out of the US. That changed: in July 2025 it acquired QCEX (QCX, LLC and its clearinghouse) for $112M, a CFTC-licensed DCM and Derivatives Clearing Organization. In November 2025 the CFTC issued an Amended Order of Designation, and Polymarket relaunched real-money trading for US users in December 2025 through that regulated entity.

The trap for US traders: the entities are not interchangeable. The international site polymarket.com still blocks US persons, and its terms prohibit VPN evasion. Trading legally from the US means using Polymarket US (the QCEX-cleared product) or Kalshi. Do not route around a geoblock with a VPN. You lose regulatory protection, and Polymarket has frozen and seized balances from accounts it identifies as US persons.

Settlement and funding

This is the sharpest practical split. Kalshi is fiat-native: debit card, ACH, and bank transfer, with funds in regulated custody and withdrawals back through the same rails. No crypto, no wallet, no gas.

Polymarket is crypto-native. The international product settles in USDC on Polygon. Deposits and withdrawals in USDC carry no Polymarket fee, and Polygon gas is typically under a cent and abstracted away by a relayer that pays it for you, so trading feels gasless. Funding via debit card through MoonPay costs roughly 2 to 3 percent, so the cheap path is buying USDC on an exchange and bridging it in. The US regulated product intermediates through traditional custody, which changes this picture, so check the funding flow for the specific entity you onboard to.

Markets offered

Both list politics, sports, economics, crypto, weather, and 'mention' markets on what public figures will say. The category mix is where they differ. Since July 2024, three categories make up about 90 percent of volume on each, but the weighting is nearly inverted:

Scale context: combined monthly volume across the two grew from under $5B in September 2025 to about $24B in April 2026 (Pew Research). Q1 2026 was a record quarter, roughly $33B on Kalshi and $26B on Polymarket. Liquidity is real on both, but it concentrates in different places, so depth on a specific contract is the thing to check, not headline totals.

Fees

Neither charges a flat commission. Both use a curved fee that peaks at 50 percent implied probability (a 50-cent price) and shrinks toward the 1-cent and 99-cent extremes, because the fee scales with p times (1 minus p). One unit warning up front: Kalshi quotes its cap in cents per contract, Polymarket's effective rates are usually quoted as a percent of price, so convert to a common unit before comparing.

Kalshi taker fee is 7 cents times C times (1 minus C) per contract, where C is the price. That tops out at 1.75 cents per contract on a 50/50 market, which is 3.5 percent of a 50-cent contract's price, and falls toward zero at the tails. Maker fees are 25 percent of the taker fee. No settlement fee, no membership fee, no ACH fee.

Polymarket on the international product applies a category-tiered taker fee using fee = C × rate × p × (1 - p). The rate coefficient runs from 0.03 on sports up to 0.07 on crypto, with politics, finance, and tech around 0.04 and economics, culture, and weather around 0.05, while world/geopolitical markets are fee-free. Note that Polymarket expanded fees to most categories on 30 March 2026; before that only crypto and sports carried them, so an older schedule will understate your cost. Makers pay no taker fee and earn a daily rebate of 20 to 25 percent of the counterparty's fee. On the US regulated exchange the structure reported is a flat 0.30 percent taker fee with a 0.20 percent maker rebate, so confirm the schedule for the exact venue you are on.

Net, stated in a common unit at the 50-cent peak: Kalshi taker is 3.5 percent of price, Polymarket's sports tier peaks near 0.75 percent and crypto near 1.8 percent, and a maker rebate (where offered) flips the math entirely if you provide liquidity. Run the numbers per contract, not per platform.

API and automation

If you are running strategies, the auth and execution models are different enough to drive integration cost.

A from-scratch bot against either is commonly a few weeks of work plus ongoing maintenance for partial fills, reconnects, and API changes. Running one strategy across both means reconciling two auth models, two settlement currencies, and two market-identifier schemes, which is most of the real friction in cross-venue arbitrage.

This is the gap Banger closes. You write one Python strategy against a single interface, paper-trade it against the live order book on either venue, then run it live with a declarative risk envelope (per-trade cap, daily loss stop, max open positions, kill switch). Banger never custodies funds. You bring your own Kalshi and Polymarket keys, and the runtime handles the per-venue auth and settlement differences so the strategy code stays the same.

# One strategy, paper-traded against the live book, then live
# pip install bangertrades

banger run momentum.py --paper --venue kalshi
banger run momentum.py --paper --venue polymarket
banger run momentum.py --live  --venue kalshi  # uses your own key

Bottom line

Both are now CFTC-regulated and legal for US persons, so the old 'Kalshi is the only legal option' line is out of date as of late 2025. Pick on substance: Kalshi for fiat rails, no crypto, and the deepest sports books; Polymarket for crypto-native settlement and deeper political and crypto markets. For developers, Kalshi is the more conventional API and Polymarket is the wallet-signed CLOB. If your edge spans both, the work is in the plumbing, which is exactly what a shared runtime is for.

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