Exchange and prediction-market fee calculator
Your real price after fees on Kalshi, Polymarket, Novig, ProphetX, BetOpenly, Betfair and more, from each venue's published fee schedule, with the cent rounding that moves small orders.
Inputs
Result
updates as you typeRun this math on every line, automatically
Every exchange and prediction-market price in our tools is shown at this net price, and EV and best price use it.
How it works
Exchanges and prediction markets don't build a margin into the price; they charge a fee, so the quoted price is better than the one you actually get. The fee models we use, from each venue's published schedule:
Kalshi: fee = ceil(0.07 × M × C × P × (1 − P)) to the cent, per order (M = series multiplier; MLB 0.5)
Polymarket US: fee = 0.0695 × C × P × (1 − P), rounded to the cent (halves to even)
Novig: no fee pregame; live and futures rates are listed in the calculator
ProphetX, Smarkets, Matchbook, Betfair: commission on net winnings: net d = 1 + (d − 1)(1 − c)
BetOpenly: 1% of the total pot from the winner: net d = d × 0.99
contract venues: net decimal = C ÷ (C × P + fee)
P is the contract price (0.55 = 55¢) and C the number of contracts. Because fees round to the cent per order, a single contract can cost noticeably more than a large order at the same price. Brokers that route to these exchanges (DraftKings Predictions, FanDuel Predicts, Fanatics Markets, Robinhood, Crypto.com) have their own tables, included where published. Where a venue does not publish its fee, we say so and never guess.
Worked example
A 55¢ contract (quoted −122.2) bought with a $100 order:
Kalshi: C = round(100 ÷ 0.55) = 182 contracts; fee = ceil(0.07 × 182 × 0.55 × 0.45) = ceil(3.1532) = $3.16
Net decimal = 182 ÷ (182 × 0.55 + 3.16) = 1.7625 → −131.1
| Venue | Quoted | Net | Break-even |
|---|---|---|---|
| Kalshi | −122.2 | −131.1 | 56.74% |
| Polymarket US | −122.2 | −131.1 | 56.72% |
| Novig | −122.2 | −122.2 | 55.00% |
| ProphetX | −122.2 | −124.7 | 55.50% |
| BetOpenly | −122.2 | −125.0 | 55.56% |
| Smarkets | −122.2 | −124.7 | 55.50% |
Order size matters on Kalshi because the fee rounds up per order: one contract at 50¢ nets −108.3, while 200 contracts net −107.3.
Things to watch
- Fees change. Venues revise schedules and promotions; our table cites the published schedule as of October 2026.
- Depth. The quoted price may cover only part of your order; the rest fills worse.
- Maker vs taker. Resting orders (maker) often pay less or nothing, but may not fill.