Prediction-market price to probability
Read a YES price as the chance the market puts on the event, and as the probability you need after Kalshi's taker fee to break even.
How the numbers are worked out
A contract pays $1 if the event happens. A price of c cents is an implied probability of c/100.
Kalshi charges a taker fee of 0.07 × contracts × P × (1 − P), rounded up to the cent, where P is the price in dollars. It is largest at 50¢ and is charged only when an order fills immediately. Most markets use this rate; some series use a different multiplier, listed on Kalshi's fee schedule. The break-even probability after fees is the price plus the fee per contract.
Polymarket's fees differ by market, so they are not included here. Check the market's own page before you trade.
When YES and NO prices add up to more than 100¢, the extra is the spread. With the spread taken out, the probability of YES is the YES price divided by the sum of both prices.
Before trading, read the market's resolution rules. They decide what counts as YES.
Build this as your own app
Tell Younna the contracts you hold, what you paid and your own estimate of each event. It builds a personal market board that reads every live price as a probability after fees, beside your estimate, and tells you when the gap crosses your line.
Younna never places trades.
See an example app on the home page →