Prediction Market Calculators
Six tools for working out what a trade actually costs and what it is actually worth. Everything runs in your browser — nothing is sent anywhere, and nothing needs an account.
Market fees
Work out what Kalshi, Polymarket and Novig actually charge on a trade, and what you keep if it lands.
Vig & no-vig
Find the margin baked into any two-sided market, and what the prices would be without it.
Expected value
Check whether a contract is worth buying at its current price, given what you think the real odds are.
Odds converter
Convert between prediction market cents, implied probability, American odds and decimal odds.
Parlay
Combine multiple contracts into one payout and see the real chance of every leg landing.
Net profit
See what actually reaches your account once platform fees and tax come out of a winning year.
What these are for
Prediction markets look simpler than they are. A contract settles at $1, so the price is the probability and the arithmetic feels obvious — right up to the point where you need to know whether Kalshi's fee formula leaves you ahead of Polymarket's percentage, or what a −140 sportsbook line is worth in cents, or how much of a 3% edge survives tax.
Each tool answers one of those, with the formula stated on the page rather than hidden. Start with market fees if you are comparing venues, or expected value if you are deciding on a specific trade.
For live prices rather than hypotheticals, our arbitrage scanner and odds comparison runs the same maths across Polymarket and Kalshi every ten minutes.
