Prediction Market Fee Comparison: Kalshi vs Polymarket vs Robinhood vs Interactive Brokers

Fees are one of the most important factors when choosing a prediction market platform. A few cents per contract may not sound significant, but at scale — or when trading frequently — fee structures materially affect returns. This comparison breaks down the cost of trading on the four major platforms available to US traders in 2026: Kalshi, Polymarket, Robinhood Sports, and Interactive Brokers ForecastTrader.

Fee Comparison at a Glance

Kalshi: Low Flat Fee, No Trading Commissions

Kalshi operates as a CFTC-designated contract market — essentially a regulated exchange. Its fee model is designed to be straightforward:

• Trading fees: None. Kalshi charges no maker or taker fees on any trade.
• Settlement fee: $0.01 per contract on winning positions. If you buy 100 YES contracts at $0.60 each and the market resolves YES, you pay $1.00 in settlement fees on your $100 payout.
• Withdrawal fees: No fee for standard ACH bank transfers. Wire transfers may incur standard bank fees.
• Minimum deposit: None. Kalshi accepts deposits as small as $1.

The settlement fee is the key cost to model. At $0.01 per contract, a trader buying 1,000 contracts on a winning position pays $10 in settlement fees. On a $600 investment (at $0.60 per contract) that pays out $1,000, that is a 1% effective fee on the payout — competitive for a regulated exchange.

Kalshi also generates revenue through the bid-ask spread on contracts, which typically ranges from $0.01 to $0.03 depending on liquidity. Liquid markets on major events (Fed decisions, election outcomes) often have $0.01 spreads.

Polymarket: Zero Fees on a Crypto-Native Platform

Polymarket charges no trading fees whatsoever — no maker fees, no taker fees, no settlement fees. This makes it the lowest explicit-cost platform in the industry.

• Trading fees: None.
• Settlement fees: None.
• Withdrawal fees: Blockchain gas fees apply when moving USDC on or off the platform. Fees depend on Polygon network congestion and are typically a fraction of a cent to a few cents per transaction.
• Minimum deposit: None, but you need USDC on the Polygon network to fund your account.

The catch: Polymarket is a crypto-native platform. Funding your account requires buying USDC, bridging it to the Polygon network, and connecting a Web3 wallet. For traders comfortable with crypto, this is straightforward. For those who are not, the onboarding friction is a real cost even if the trading fees are zero.

Polymarket is also not available to US residents under its current terms of service. It operates globally and primarily serves international traders. US residents who access Polymarket do so at their own legal risk.

Robinhood Sports: No Fees, Seamless Onboarding

Robinhood Sports offers prediction market contracts with no explicit fees. Robinhood partners with Kalshi's exchange infrastructure but presents a distinct interface and user experience.

• Trading fees: None.
• Settlement fees: None (Robinhood absorbs or passes through Kalshi settlement fees internally).
• Withdrawal fees: No fee for ACH transfers to a linked bank account. Standard Robinhood instant transfer options may apply.
• Minimum deposit: None.

Robinhood's revenue model relies on payment for order flow and the spread in contract pricing. In practice, Robinhood contracts often have slightly wider spreads than trading directly on Kalshi, which represents a hidden cost.

The key advantage is distribution. If you already have a Robinhood account, you can start trading prediction markets in seconds — no new account, no new funding, no new KYC. For users already in the Robinhood ecosystem, this zero-friction onboarding is a meaningful benefit even if spreads are marginally wider.

Interactive Brokers ForecastTrader: Commissions Apply

Interactive Brokers ForecastTrader integrates prediction market contracts directly into the IBKR brokerage platform. Unlike the other three platforms, Interactive Brokers does charge commissions on prediction contract trades.

• Trading fees: IBKR's standard commission structure applies. For most US retail clients on the IBKR Lite plan, equity trades are commission-free, but event contracts (prediction markets) are subject to commissions — typically $0.65 per contract with a $1.00 minimum, similar to options commissions.
• Settlement fees: None.
• Withdrawal fees: None for standard ACH transfers.
• Minimum deposit: IBKR has no formal minimum for retail accounts, though many features require funding above $10,000.

The commission structure makes Interactive Brokers significantly more expensive for frequent prediction market trading. A trader buying 50 contracts pays at least $1.00 in commissions — equivalent to 100 settlement fee-paying contracts on Kalshi.

Where IBKR excels is for existing clients who want to incorporate prediction market contracts into a broader portfolio without opening a separate account. If you already use IBKR for stocks, bonds, and options, adding prediction market exposure without a new account or wire transfer is convenient. The IBKR platform also provides more sophisticated order types and portfolio analytics than purpose-built prediction market platforms.

Hidden Costs: Spreads and Slippage

Trading fees and settlement fees are the explicit costs, but bid-ask spreads represent an implicit cost on every trade. In liquid markets, spreads on Kalshi and Polymarket can be as tight as $0.01. In illiquid markets or during volatile events, spreads can widen to $0.05 or more.

Robinhood consistently shows slightly wider spreads than Kalshi direct because of how order routing works through its partnership arrangement. For small trades (under 100 contracts), this difference is negligible. For larger positions, direct Kalshi trading often produces better execution.

Which Platform Is Cheapest?

For most US traders, Kalshi offers the best combination of low fees and regulatory protection. The $0.01 settlement fee is the only explicit cost, spreads are tight on major markets, and the platform is fully CFTC-regulated.

Robinhood Sports is effectively free for casual traders and is the right choice if you prioritize onboarding simplicity over execution quality.

Polymarket is technically the cheapest on fees (zero explicit costs), but US residents cannot legally use it and the crypto onboarding is a barrier.

Interactive Brokers is the most expensive option for prediction market trading specifically, but makes sense for existing IBKR clients who want to add prediction market exposure without managing a separate account.

For a detailed side-by-side platform comparison, see Kalshi vs Polymarket vs Robinhood or Kalshi vs Interactive Brokers. To start trading, visit the live odds page to see current market prices.