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Bet Hero prediction market calculator: what it does, what it costs, where it stops
Last checked 2026-09-08
Bet Hero Sports is a sports analytics site with a single prediction market calculator page covering Kalshi, Polymarket, PredictIt and a Custom fee option. You pick the platform, the order type (Taker or Maker), a price from 1 to 99 cents and a contract count, and it returns implied probability, decimal and American odds, net profit and effective odds after fees.
It is the rare calculator that prints its Kalshi fee formula on the page, which makes it auditable in a way the range-only calculators are not.
What it does
The page states the Kalshi taker fee as fee = ceil(0.07 x contracts x P x (1 minus P)), and explains that fees are highest at 50 cents and shrink toward the extremes. That is the parabolic schedule Kalshi publishes, and it is why a 50-cent contract costs more in fees than a 90-cent one.
For PredictIt it applies the 10% charge on profits from winning contracts and notes the 5% withdrawal fee. For Polymarket the page states there are no explicit trading fees and that costs sit in the bid-ask spread.
- Inputs: platform (Kalshi, Polymarket, PredictIt, Custom), order type, price in cents, number of contracts
- Outputs: implied probability, decimal and American odds, net profit, effective odds after fees
Pricing
Free. Bet Hero states it is not a casino, sportsbook or gambling operator and does not accept or place wagers.
Venues and data
Three named venues plus a Custom slot where you type your own fee rate. No live prices are pulled in.
Where it falls short
The Polymarket treatment is the weak point. The page models Polymarket as fee-free, while other calculators model a taker fee and maker rebate on Polymarket's U.S. exchange. Which one applies depends on which Polymarket you trade, and the page does not draw that distinction. Check the venue's current schedule before trusting the Polymarket output.
It is one calculator, not a suite. There is no Kelly, hedge, parlay or arbitrage tool on the prediction market page; those live on the sportsbook side of the site.
Who should use it
A Kalshi trader who wants to see the fee formula rather than trust a black box, and who needs nothing beyond single-position payout math.
Questions about Bet Hero prediction market calculator
Is the Bet Hero prediction market calculator free?
Yes. It runs in the browser with no account.
What Kalshi fee formula does Bet Hero use?
The page states fee = ceil(0.07 x contracts x P x (1 minus P)) for taker orders, with fees peaking at 50 cents and falling toward 1 and 99 cents.
Does the Bet Hero calculator handle Polymarket fees?
It treats Polymarket as having no explicit trading fee, with costs in the spread. That does not match calculators that model a taker fee on Polymarket's U.S. exchange, so confirm which venue and schedule apply to you.
Does Bet Hero place trades?
No. The site states it is not a casino, sportsbook or gambling operator and does not accept or place wagers.
Trackers find the edge. Calculators size it. Alerts time it.
When it is time to execute, the free Kairos terminal trades Kalshi, Polymarket and Predict.fun from one book.