Prediction market fee calculator

What it computes

The fee on one fill: pick a venue and, where its schedule splits, the category, series or route; pick taker or maker; enter the price in cents and the number of contracts. You get the fee in dollars, the same fee per contract, and the fee as a share of what the contracts cost you, which is contracts times price. A negative fee is a maker being paid.

Below it is the same fill on every schedule the page models, lowest fee first, and the venues it does not model, each with the figure its card does give. The default — a Kalshi taker buying 100 contracts at 50 cents on a standard series — is the trade the cards' fee fields describe; see the effective fee at fifty cents for why the catalogue compares venues at that one price, and what a trade actually costs for the four bases venues publish fees on.

Where the numbers come from

Every rule is the one the venue's card quotes from the venue's own schedule, with the card's rounding, and every source below is the document the card read, with its date or the day it was read. The rules live in one table that this page and its Markdown twin both read, so the twin prints every coefficient, flat rate and rounding rule next to its document.

• A curve. Coefficient × contracts × price × (1 − price): Kalshi at 0.07 for takers, with 0.0175 for makers on the series that carry maker fees and 0.035 on combination markets; Polymarket at 0.07, 0.05, 0.04 or nothing by category, makers never charged; Polymarket US at 0.0695 for takers and −0.0125 for makers, 0.10 for takers on table tennis; Gemini Predictions at 0.07 and 0.0175 on contracts listed from 18 March 2026; Novig at 0.03 to 0.10 by trade type, nothing before the game; Underdog Predict at 0.07 and 0.0175 on its own exchange.
• The older Gemini curve. Coefficient × contracts × the lesser of price and one minus price, 0.05 and 0.01, for contracts listed before 18 March 2026.
• Flat cents. ForecastEx at a cent a contract on each side; Webull at a cent of commission and a cent of Kalshi exchange fee; PrizePicks Predict by its full table, two cents from 4 cents up.
• A capped curve plus a cent. Robinhood at 0.10, or 0.05 with Gold, capped at a cent a contract, plus the KalshiEX exchange fee of a cent; Underdog's Kalshi route at a cent of commission plus Kalshi's own fee.

Rounding is the venue's where its card states it: up to the next cent on Kalshi, Gemini, Robinhood, PrizePicks and Underdog's Kalshi route; to the nearest cent, ties to even, on Polymarket US and Underdog's UDX. Where a card states none, the fee is shown unrounded.

What it leaves out

• Venues with a fee figure and no rule. Crypto.com (1.75 and 0.44 cents a contract at 50 cents) and Futuur (1.25 and nothing) state formulas on their cards but cite no fee document to date them against. DraftKings (2 and 2) is a per-cent table of which the card holds a sample. FanDuel Predicts (2 and 2) publishes one sentence and no worked example. Limitless (1.5 and nothing) publishes its order-book curve as points. Myriad (0.5 and nothing) sets the fee market by market.
• Venues with no per-fill fee to compute. Coinbase publishes no price at all. PredictIt takes 10% of profit, with 3% on card deposits and 5% only on a withdrawal from an account idle for a year, and ProphetX 2% of net gains at settlement; neither is a fee on a fill at a price.
• Charges off the fill. Kalshi's debit-card deposit fee of up to 2%, and its reserved right to charge 0% to 2% on any rail; Myriad's 0.0085 dollars a transaction for gas; Futuur's withdrawal network fee; an on-ramp's own charge for buying the stablecoin Polymarket settles in.
• Rebates and credits. Polymarket's daily maker rebate pool and tiered taker rebate, Novig's Maker Credit Program, Polymarket US's volume-tier taker rebates, Gemini's maker rebate programme and promotions. They are paid later, from a pool or by a programme the venue can change, and none of them lowers the fee on the fill.
• Parts of a schedule. Kalshi's per-series multiplier, left at its default of 1 although 155 series differ and some are free; Polymarket US's steeper combo curve; Robinhood's CME, ForecastEx and Rothera routes, whose exchange fee the schedule does not quote; the regulatory fees Underdog passes through on its Kalshi route; any exchange fee on top of PrizePicks' commission; the perpetual futures Kalshi and Polymarket now also run.
• Rounding across fills. Gemini rounds per fill and Underdog per trade, so an order that fills in five pieces is rounded five times, and where the rounding is up that can cost up to a cent a piece more than one fill of the same size. The page rounds the order as one fill. Kalshi's schedule also defines its round-up in a gloss as fee plus position cost to a hundredth of a cent; the figures here follow its worked table, to the cent.
• The round trip and the spread. Closing before settlement pays the fee again, at the exit price. What you give up crossing the spread can be more than the fee, and appears in no schedule.
• A trading client's own cut. Bots and terminals charge on top of the venue — Kreo, PolyCop, PolyBot, Polycool, Stand and Kairos among them. Their rates are on their cards.
• Interest on collateral. ForecastEx passes interest on collateral to members as a monthly coupon, which offsets a fee over a long hold and is not a fee at all.