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Prediction Market Fee Calculator: Compare Trading Costs
Last Updated: March 4, 2026
Trading fees determine how much profit you actually keep. The calculator above models the exact cost of any prediction market trade across Polymarket, Kalshi, and other platforms. Enter your trade parameters — contract price, position size, and platform — to see the fee in dollars, the net return, and the side-by-side comparison. Fees that look small in percentage terms can materially change whether a trade is worth making.
How Do You Use the Fee Calculator?
Enter three inputs: the contract price (probability), the number of contracts or dollar amount, and the platform. The calculator returns the explicit fee, the net payout if the trade wins, the net return percentage, and a comparison across platforms.
The key output is net return after fees — not the gross payout. A contract bought at $0.80 that resolves to $1.00 looks like a 25% return. After Polymarket’s 2% fee on the $0.20 profit, the net return drops to 24.5%. After Kalshi’s per-contract fee on both entry and exit, the net return might be 23% or lower depending on the fee tier. These differences compound across dozens of trades.
How Do Fee Structures Differ Across Platforms?
Each prediction market charges differently. The structure determines which platform is cheaper for a given trade.
| Platform | Fee Type | Rate | When Charged | Cost on $100 Position at 50% |
|---|---|---|---|---|
| Polymarket | % of winnings | ~2% | Settlement (winning trades only) | ~$1.00 |
| Kalshi | Per-contract | 1-2 cents | Entry and exit | ~$1.00-$2.00 |
| Metaculus | None | Free | N/A | $0 (reputation-based) |
The crossover point matters. For contracts above ~$0.70, Polymarket’s percentage fee applies to a small profit margin, making it cheaper in absolute dollars. For contracts below ~$0.30, the profit margin is large, and 2% of a big win costs more than Kalshi’s flat fee. The calculator models this crossover precisely for your specific trade.
For a full breakdown of how each platform’s fee structure works, see how prediction market fees work.
What Does a Fee Comparison Look Like in Practice?
Consider buying 200 contracts at $0.35, expecting the event to occur.
| Metric | Polymarket | Kalshi |
|---|---|---|
| Entry cost | $70.00 | $70.00 + ~$2.00 entry fee |
| Gross payout if win | $200.00 | $200.00 |
| Gross profit | $130.00 | $128.00 |
| Platform fee | $2.60 (2% of $130) | ~$2.00 exit fee |
| Net profit | $127.40 | $126.00 |
| Net return | 182.0% | 175.0% |
At the $0.35 price point, the platforms cost roughly the same. Move the contract price to $0.80 and the comparison shifts. Polymarket’s 2% of a $0.20 profit ($0.80 per 200 contracts) undercuts Kalshi’s flat fee. Move to $0.10 and Kalshi’s flat fee is cheaper than Polymarket’s 2% of $0.90 profit ($3.60 per 200 contracts).
The calculator runs these scenarios instantly for any contract price and position size.
How Do Fees Change the EV of a Trade?
Fees reduce the net payout, which directly reduces expected value. The effect is proportionally larger on high-probability, low-margin trades.
A contract at $0.85 with a true probability of 90% has a gross EV of:
- EV (before fees) = (0.90 x $0.15) - (0.10 x $0.85) = $0.135 - $0.085 = +$0.05
After Polymarket’s 2% fee on the $0.15 profit:
- Net profit = $0.15 - $0.003 = $0.147
- EV (after fees) = (0.90 x $0.147) - (0.10 x $0.85) = $0.132 - $0.085 = +$0.047
The fee reduced EV by 6%. On thinner edges — a true probability of 87% instead of 90% — fees can flip a marginally +EV trade to -EV entirely. Use the EV calculator alongside the fee calculator to model net expected value before committing capital.
What Hidden Costs Add to Explicit Fees?
The calculator models explicit platform fees. Implicit costs add to the total: bid-ask spreads (1-2 cents on liquid Polymarket markets, 5-10 cents on thin Kalshi markets), currency conversion (0.5-1.5% to buy USDC for Polymarket), and capital lockup on long-duration contracts. A 5-cent spread on a $0.50 contract is a 10% round-trip cost — far larger than either platform’s explicit fee.
The Odds Reference dashboard tracks live spreads and prices across platforms, giving you visibility into implicit costs alongside the explicit fees the calculator models.
How Should Fee Structure Influence Platform Choice?
The optimal platform depends on the trade profile:
- High-probability contracts ($0.70+): Polymarket’s percentage-based fee is small in absolute terms — often the cheaper option
- Low-probability, high-payout trades ($0.05-$0.30): Kalshi’s flat per-contract fee costs less than Polymarket’s 2% of a large profit
- Frequent traders: Kalshi’s predictable flat fee is easier to model across a portfolio; Polymarket charges nothing on losing trades
- Non-US or crypto-native traders: Polymarket avoids banking friction entirely
For a head-to-head breakdown of these platforms beyond fees, see the Polymarket vs Kalshi comparison and the broader platform comparison.
Key Takeaways
- Polymarket charges ~2% of winnings at settlement; Kalshi charges 1-2 cents per contract on entry and exit — each favors different price points
- The crossover point is around $0.50-$0.70: Polymarket is cheaper above it, Kalshi below
- Fees directly reduce expected value — always calculate EV after fees to assess true profitability
- Hidden costs (spreads, currency conversion, capital lockup) often exceed explicit fees on thin markets
- The fee calculator models exact costs before you trade; the EV calculator confirms whether the trade remains profitable after those costs