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Trader Tools · The Fee Truth
A 63¢ contract does not break even at 63% — venue fees push your true breakeven higher. This calculator applies Kalshi’s trading-fee formula (0.07 × contracts × P × (1−P)) or Polymarket’s winnings fees to show the probability your position actually needs.
64.6%
Fee-adjusted breakeven
the true probability must exceed this for +EV (+1.6pts of fee drag)
$64.64
Total cost
$63.00 stake + $1.64 trading fee
+$35.36
Profit if YES
−$64.64 if NO
Payout anatomy — if YES hits
100¢ / contract
Formulas: Kalshi trading fee = 0.07 × contracts × P × (1−P), rounded up to the cent. Breakeven = total cost ÷ net payout. Fee schedules change — verify on the venue before trading. Educational tool, not advice.
Prediction-market YES/NO pairs price to ~100¢ with no bookmaker vig — the cost sits in venue fees instead. Kalshi charges at trade time with a formula that peaks at 50¢ prices; Polymarket is fee-free on most markets but applies winnings fees on some. Either way, your edge has to clear the fee drag before it is real: that is the number this tool computes. Convert prices with the odds converter, or check whether a cross-venue gap survives fees with the arbitrage checker.
Kalshi’s standard trading fee is 0.07 × contracts × P × (1−P), rounded up to the next cent, where P is the price in dollars — so fees are highest for 50¢ contracts (maximum uncertainty) and shrink toward the extremes. On 100 contracts at 63¢ that is about $1.64. Always verify the current schedule on Kalshi, as some markets carry different rates.
Polymarket charges no trading fee on most markets. Some markets — notably certain sports markets — carry a fee on winnings; the market’s own rules page states it. This calculator lets you set a winnings-fee percentage to model it.
It is the true probability at which your position stops losing money in expectation: total cost (stake + trading fees) divided by net payout (winnings minus any settlement fee). Buying at 63¢ with fees might carry a 64.7% breakeven — the market has to be more than ~1.7 points "wrong" in your favor before you have an edge.
Educational tool, not advice. Fee schedules change — verify on the venue before trading.