Kalshi fees, explained

1 · The formula

Kalshi charges a per-trade fee that scales with how “coin flip” the contract is. It peaks at 50¢ and shrinks to almost nothing at the edges:

The price × (1 − price) shape is mathematically the variance of a single Bernoulli trial. Kalshi’s pricing it like an options-style fee that’s proportional to how uncertain the outcome is right now. Cheap (5¢) and near-certain (95¢) contracts cost almost nothing to trade. A 50¢ coin-flip is the maximum.

2 · What it works out to in real prices

At a 50¢ price the fee is 1.8¢ per contract, or 3.5% of the trade. At a 5¢ price it’s 1¢ per contract (the minimum), but that’s 20% of the trade — for very cheap contracts the minimum-fee floor dominates. Worth remembering when scanning for small-edge arbs on long-shot markets: the fee can eat the whole edge.

3 · A worked trade

Buy 100 contracts of YES on a Kalshi market at 46¢:

The all-in cost-per-share is $0.4774. That’s the number that matters when you’re computing the cross-exchange arb: it’s the “real” price you paid, not the quoted 46¢.

4 · Fees on settlement / withdrawal

Kalshi doesn’t charge a separate settlement fee — winnings credit to your balance with no additional cut. ACH withdrawals are free, with the usual 1–3 business day clearing. Wire and debit-card payout methods may have small bank-side fees. The per-trade fee above is the only Kalshi-side cost you need to model when sizing an arb.

5 · Quick rule of thumb

For mental math: at mid-market prices (30¢–70¢), the Kalshi fee costs ~3–4% of your stake per side. So a cross-exchange arb needs roughly 4% of combinedraw edge before fees just to break even on the Kalshi leg alone — plus Polymarket’s 2% of winnings on the other side. Total “tax” on a mid-market arb is usually 4–6 cents per dollar of guaranteed payout. That’s why arbs above ~1% net edge are rare.