The quick version
Prediction-market fees are not one flat number
A prediction-market contract pays $1.00 if it settles in your favour and nothing if it does not, so its price in cents doubles as its implied chance. The fee you pay to buy it is set by the venue’s own formula — and those formulas differ. Most are proportional to price × (1 − price), which means the fee is largest on a 50¢ coin-flip contract and smallest on deep favourites and long shots. Others, like DraftKings, charge a flat amount per contract that steps by price band. Comparing platforms on a single “fee percentage” hides these differences.
Trading fee, funding cost and spread are three different things
The trading fee is what the exchange charges to open or close a position. A funding cost is what your card, bank or crypto network charges to move money in or out — Kalshi ACH transfers are free while a card deposit can add up to about 2%. The bid–ask spread is an execution cost you pay by crossing the market to trade immediately. This calculator keeps them separate: the headline number is the trading fee only, funding appears on its own line when you enter it, and spread is never silently added to a hold-to-settlement result.
Break-even probability is the number that matters
The clearest way to see a fee’s impact is what it does to your break-even point. Buy 100 Kalshi contracts at 50¢ and the $1.75 taker fee lifts your total cost to $51.75, so the contract now has to win more than 51.75% of the time — a 1.75-point shift — just to break even when held to settlement. That framing travels across platforms far better than a raw dollar fee, because it folds the price and the fee into a single, comparable threshold.
Why our number can differ from your order preview
We model each platform’s published schedule with its primary source and the date we last checked it, but a live order preview is always the final word. Schedules change, and your exact fee depends on the series, category, account tier or venue exchange fee that applies at the moment you trade. Slippage, a moving market price, user-specific rebates and taxes are deliberately out of scope. When a platform’s public inputs do not support a reproducible calculation, we leave it out rather than guess.