Prediction market pricing looks nothing like a sportsbook line, and the fee structure changes depending on which exchange holds the contract. Entering the number of contracts, the price per contract, and the exchange turns a raw position into cost, fee, payout, profit, return, and an equivalent American price, so a bettor knows exactly what a position pays before money is committed.
One hundred contracts at 40 cents on Kalshi cost $40.00, but the exchange fee brings total outlay to $41.68. If the contract resolves yes, it pays $100.00, for a profit of $58.32 and a return of 139.9%. Converted to a sportsbook price, that’s +140, with a break-even probability of 41.7%.
Three inputs drive the result. First, the number of contracts being bought. Second, the price per contract in cents, since prediction markets quote in cents rather than dollars. Third, the exchange: Kalshi, Polymarket, Robinhood, or a no-fee option for markets that don’t charge one.
The result lays out cost, the fee charged by that exchange, total outlay, and the payout if the contract resolves yes. Below that sits profit, return on outlay as a percentage, the effective American odds the position works out to, and the break-even probability required to turn a profit. A bettor can change the exchange without touching contracts or price to see how the fee alone shifts the numbers.
Cost is contracts times price: 100 contracts at 40 cents is $40.00. Kalshi charges 7% of expected profit per contract, rounded up to the cent, which comes to $1.68 on this position, bringing total outlay to $41.68. Robinhood instead charges a flat one cent per contract regardless of price, and Polymarket charges nothing on most markets.
Every contract pays $1.00 if the market resolves yes, so 100 contracts pay $100.00. Profit is payout minus cost minus fee: $100.00 minus $40.00 minus $1.68 equals $58.32, a 139.9% return on the $41.68 outlay. Dividing profit by outlay gives the effective American price of +140, and dividing outlay by payout gives the break-even probability of 41.7%, the minimum chance of a yes resolution needed to profit.
The number matters most when the same market trades on more than one exchange at close to the same price. A Kalshi fee eats into profit in a way a Polymarket position at the identical price does not, so two contracts that look the same at a glance can pay different amounts after fees.
The common mistake is judging a position by price alone and ignoring the fee entirely, or assuming Robinhood’s flat per-contract fee behaves the same way as Kalshi’s percentage-based one at every price point. A sharp bettor runs the position through each exchange it trades on, compares the resulting break-even probability to their own estimate of the true chance, and places the contracts wherever the fee leaves the most room between the two.
What’s the difference between Kalshi’s fee and Polymarket’s? Kalshi charges 7% of expected profit per contract, rounded up to the cent, so the fee grows with position size and moves with price. Polymarket charges nothing on most markets, so the payout and profit calculated at a given price are usually the final numbers with no fee subtracted.
Why does the break-even probability matter? It states the minimum chance of a yes resolution needed just to cover cost and fee. A position with a break-even probability of 41.7% only turns a profit if the true chance of yes is higher than that, so comparing the number to an independent estimate is how a bettor checks whether the price offers value.
How does the effective American price help compare to a sportsbook? Prediction markets quote in cents, not odds, so converting profit divided by outlay into a number like +140 lets a bettor line that position up against a moneyline on a sportsbook pricing the same outcome, using one common scale instead of two.
Does the fee change if the position size changes? On Kalshi, yes, since the fee is a percentage of expected profit per contract and scales with the number of contracts and the price paid. On Robinhood, the fee is a flat cent per contract, so it scales only with contract count, not price.