Prediction market fee calculator: what a Kalshi or Polymarket order costs before it fills

Free tool · Updated October 26, 2026 · 18+ · Not trading advice · By BetG8

Neither of the two big US prediction markets charges a flat percentage. Both charge a fee that depends on the price of the contract, peaks at 50 cents and shrinks towards 1 cent and 99 cents, and both treat an order that fills immediately differently from one that rests on the book. That makes the cost of a trade hard to see on the order ticket. Enter the number of contracts, the price and the order type below and the calculator returns the Kalshi fee from its published formula and the Polymarket fee for the market category you choose, side by side, with the all-in cost per contract, the fee as a share of the stake and the probability the event needs to beat for the purchase to break even. Add an exit price and it also prices a round trip.

How it works

Both venues build the fee on the same term, price times one minus price. A contract at 50 cents has the most uncertainty in it, and P × (1 − P) is largest there at 0.25; at 10 cents or 90 cents it is 0.09. Kalshi multiplies that term by 0.07 for takers, so 100 contracts at 50 cents cost 0.07 × 100 × 0.25 = $1.75, the most a Kalshi taker pays per contract. Polymarket multiplies the same term by a rate that depends on the category of the market, so the same 100 contracts cost $1.25 on a sports market and $1.00 on an election market. The calculator applies both formulas to your inputs, adds the fee to the price to get the all-in cost per contract, and divides by $1, the payout of a winning contract, to give the break-even probability.

The last column is the one most people miss. In dollars the fee is highest at 50 cents, but against the money at risk it is heaviest on cheap contracts: 6.3 percent of the stake at 10 cents against 0.7 percent at 90 cents. A trader who buys longshots pays proportionally more than one who buys favourites, on both venues.

A worked example

Take 200 contracts bought at 35 cents as a taker, a $70 stake. On Kalshi the fee is 0.07 × 200 × 0.35 × 0.65 = $3.185, rounded up to $3.19, so the order costs $73.19, or 36.6 cents a contract, and the event has to happen more than 36.6 percent of the time to break even. On a Polymarket sports market the fee is 0.05 × 200 × 0.35 × 0.65 = $2.275, the order costs $72.28 and the break-even probability is 36.1 percent. On a Polymarket politics market the fee falls to $1.82. Placed as a resting order that later fills, the same purchase costs $0.80 on a Kalshi series with a maker multiplier of 1, nothing on an unlisted Kalshi series and nothing on Polymarket. If you then sell the 200 contracts at 50 cents before settlement, Kalshi charges a second taker fee of $3.50, because 50 cents is the peak of the curve.

Limits

The calculator covers trading fees on standard event contracts and nothing else. It does not include the bid-ask spread, which on a thin market can cost more than the fee; deposit and withdrawal charges, such as Kalshi's fee of up to 2 percent on debit card deposits; or any commission a broker adds when you reach either exchange through another app. Kalshi's schedule sets a multiplier for each series, a short list of series is fee-free, and the schedule's rounding rule can differ from the next-cent rounding used here by a fraction of a cent on some orders. Polymarket rounds fees to five decimal places and pays part of its taker fees back to makers as rebates, which the calculator does not model. Rates are from Kalshi's fee schedule effective July 7, 2026 and Polymarket's fee documentation as read in October 2026; both change, and the live schedules govern. The tool does arithmetic on the numbers you enter. It is not a recommendation to trade on either venue, and access to both depends on your state.

FAQ

How is the Kalshi trading fee calculated?

For a taker order Kalshi charges 0.07 × contracts × price × (1 − price), with price in dollars, rounded up. 100 contracts at 50 cents cost $1.75 in fees, the maximum per contract. A resting maker order uses 0.0175 instead of 0.07 on series where a maker fee applies and pays nothing on the others.

How is the Polymarket trading fee calculated?

Polymarket charges takers shares × fee rate × price × (1 − price), where the rate depends on the market category: 0.07 for crypto, 0.05 for sports, economics, culture, weather and other markets, 0.04 for politics, finance, tech and mentions, and 0 for geopolitics. Makers pay no fee.

Which is cheaper for a 100-contract order at 50 cents?

As a taker, Kalshi charges $1.75. Polymarket charges $1.25 on a sports market, $1.00 on a politics market, $1.75 on a crypto market and nothing on a geopolitics market. As a maker, Polymarket is free and Kalshi charges at most $0.44.

What does the break-even probability mean?

It is the all-in cost per contract, price plus fee, read as a probability. If a contract costs 35 cents plus a 1.6-cent fee, the event has to happen more than 36.6 percent of the time for the purchase to break even before any spread.

Related

• Kalshi fees explained: the taker formula and maker fees
• Kalshi vs Polymarket fees compared
• Expected value explained: the one number behind every bet
• Sportsbook vs exchange price comparison tool
• Is Kalshi legal in your state? The 50-state tracker

Sources

• Kalshi, Fee schedule, last updated and effective July 7, 2026, for the taker and maker formulas, the multipliers and the deposit charges.
• Polymarket, Fees documentation, for the taker formula, the category rates, maker rebates and rounding.
• BetG8, Kalshi fees explained and Kalshi vs Polymarket fees, for the worked examples. Table figures are BetG8 calculations from the formulas above.

18+. This tool performs arithmetic on numbers you enter. It is not legal, tax, financial or betting advice. If gambling stops being fun, help is available at 1-800-GAMBLER.

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