How the fees work
Both venues charge a fee that scales with how uncertain the contract is: it is highest at 50¢ and shrinks toward zero as the price approaches 1¢ or 99¢. The fee is charged on each trade, not at settlement, so a position you sell before resolution pays twice.
Kalshi
Taker orders (filled immediately) pay round up(M × 0.07 × C × P × (1 − P)). Maker orders (left resting on the book) pay round up(M × 0.0175 × C × P × (1 − P)), but the maker multiplier M is 0 by default, so most markets charge makers nothing. A published list of series sets M to 1 for makers (for example Fed, CPI and GDP markets), sets both multipliers to 0 for fee-free series, and doubles the taker fee on combos. 100 contracts bought at 50¢ on a standard market cost $1.75 in fees; at 90¢ the same order costs $0.63. Source: Kalshi fee schedule (PDF).
Polymarket
Takers pay C × rate × p × (1 − p) with the rate set by category: 7% for crypto, 5% for sports, economics, culture, weather and other markets, 4% for politics, finance, tech and mentions, and nothing on geopolitics. Makers are never charged and receive a share of taker fees as rebates. Source: Polymarket fee docs.
Reading the result
| Field | Meaning |
|---|---|
| Break-even probability | (cost + fee) ÷ payout. The event needs at least this probability for the trade to be worth it. |
| Edge after fees | Your estimate minus the break-even probability. Negative means the fee ate your edge. |
| Expected value | Your estimate × payout − total outlay. The average result if you could make this trade many times at your estimate. |
The useful question is not “is the fee big?” but “is my edge bigger than the fee?”. Near 50¢ a taker on Kalshi gives up 1.75¢ per contract, so an estimate 2 points above the price is barely enough; at 90¢ the fee is 0.63¢ and a small edge survives. Where a market is listed on both venues, the cheaper fee is sometimes worth more than a slightly better price.
Frequently asked questions
How are Kalshi trading fees calculated?
Kalshi charges fees = round up(M × 0.07 × C × P × (1 − P)) on orders that fill immediately, where C is the number of contracts, P is the price in dollars and M is a per-market multiplier that defaults to 1. Resting (maker) orders pay round up(M × 0.0175 × C × P × (1 − P)) only on series where the maker multiplier is 1; it is 0 by default. Fees peak at 50¢ and fall toward zero near 1¢ and 99¢.
How are Polymarket trading fees calculated?
Polymarket charges takers fee = C × rate × p × (1 − p), where the rate depends on the market category: 7% for crypto, 5% for sports, economics, culture, weather and other markets, 4% for politics, finance, tech and mentions, and 0% for geopolitics. Makers are never charged.
What is the break-even probability?
The probability the event has to have for your trade to make money after fees: (contract cost + fee) ÷ payout. If you think the true probability is above the break-even number, the trade has positive expected value at your estimate.
Do I pay a fee when a contract settles?
No. Neither Kalshi nor Polymarket charges a settlement fee. You pay a trading fee when you open a position and again if you sell it before settlement.
New to reading prices as probabilities? Start with what a 72¢ contract means and how the Kalshi order book works, or compare the platforms.