Prediction market calculator

Prediction markets like Kalshi and Polymarket sell contracts that pay $1 if something happens, and charge a fee on each trade. Enter a price to see what it costs with the fee, the American odds that works out to, and how it compares with a sportsbook.

Price per contract (cents)Yes or No, 1 to 99 Contracts Fee rateKalshi takers: 7%. No fee: 0

Total cost

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price + fee

Fee

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Pays if right

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$1 a contract

Profit if right

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American odds, with the fee

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Without the fee

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Cost per contract

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= implied probability

Fee

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as a share of the price

Contracts cost before the fee.

Compare with a sportsbook

Sportsbook odds on the same resultAmerican, decimal or fractional

How it works

Prices are probabilities

A contract pays $1 if it's right and nothing if it's wrong, so its price is the market's probability: 55¢ is 55%. As American odds that's -122 before fees. Buying Yes at 55¢ is like a bet at -122; buying No at 45¢ is like a bet on the other side at +122.

The fee

Prediction markets such as Kalshi and Polymarket charge rate × contracts × price × (1 − price), worked out here rounded up to the next cent. Only the rate differs. At Kalshi's 7% taker rate, 100 contracts at 55¢ cost $55.00 plus a $1.74 fee: $56.74, or -131 in odds.

Which rate?

Kalshi charges 7% on orders that fill straight away (takers). Orders that rest on the book (makers) pay nothing on most markets, and 1.75% on the ones Kalshi lists as charging makers. Polymarket's rate depends on the market's category and has changed several times; its makers pay nothing. Use the rate on the platform's fee schedule for your market, or 0 if there's no fee.

Where the fee bites

The fee is largest in cents near 50¢ (1.75¢ a contract at Kalshi's 7%) and shrinks toward 1¢ and 99¢. As a share of what you pay it's highest on cheap contracts: about 6.7% of the price at 5¢, against 0.7% at 90¢.

Against a sportsbook

Compare odds after the fee, not the screen price. BetSharp's Kalshi prices already include an estimate of Kalshi's taker fee, so they line up with the sportsbooks' odds on every game page; see how we show Kalshi prices. Use the no-vig calculator to see a fair price for either.

The price you pay

You buy at the ask, which is usually a cent or more above the last trade or the midpoint, and Yes plus No asks usually add up to more than $1. Selling before the result is known is a trade too, charged a fee in the same way. Fees change: check the platform's fee schedule for the market.

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For information only: check every figure with your sportsbook or exchange before you bet. Calculators can't make a bet a good one, and only bet what you can afford to lose.