Calculate EV and optimal sizing for Polymarket positions, accounting for the per-category taker fee.
Polymarket charges takers a per-category fee at trade: fee = C × feeRate × p × (1−p), with feeRate 0.04 for politics and finance, 0.05 for sports, and 0.07 for crypto. The fee is charged on both winning and losing positions and peaks at $0.50, so your EV calculation subtracts the taker cost up front. Makers who post limit orders pay $0.
Enter the Polymarket contract price and select Polymarket.
Choose the market category to apply the correct fee rate.
Input your true probability estimate.
Review the EV including fee adjustments.
Check the Kelly sizing. It accounts for the taker fee.
Polymarket politics Yes at $0.35, true probability 45%. Taker fee = 0.04 × 0.35 × 0.65 = $0.0091 per share, charged at trade. Effective cost = $0.3591. EV = (0.45 × $1.00) − $0.3591 = +$0.091/share. Makers who post a limit order pay $0, raising EV to +$0.100/share.
Fee model: Per-category taker fee: fee = C × feeRate × p × (1−p). 0.05 sports, 0.07 crypto, 0.04 politics/finance. Makers pay 0.
Formula: C × feeRate × p × (1 - p); feeRate 0.04–0.07 by category (sports 0.05 as of Jul 2026)
Timing: Charged at time of trade
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