Free tools

Calculators that do the boring part

Everything here runs in your browser, needs no account, and stays free. Built because we needed them ourselves.

Live market radar

Biggest 24h movers and deepest books across Polymarket and Kalshi, pulled from the exchanges' public APIs every hour.

For: Anyone who wants to see what the crowd is betting on right now, without opening an exchange account.

Payout, net result, ROI and break-even win rate for any contract price — with Kalshi's exact fee formula applied.

For: Anyone about to buy a contract who wants to know what they actually get back if it wins.

Probability ↔ contract price ↔ American ↔ decimal ↔ fractional. For anyone moving between sportsbooks and prediction markets.

For: Sportsbook users trying to read a 62¢ contract, and market users reading a −150 line.

How much to actually put on an edge, with full, half and quarter Kelly — plus where the formula quietly betrays you.

For: Anyone who has an opinion on a market and wants to know how much of it to bet.

Does that Polymarket–Kalshi price gap survive fees? Locked spread, ROI and the minimum viable gap.

For: Anyone who noticed the same event priced differently on two exchanges.

The probability of a chain of events that each depend on the previous one — and the price at which the chain is worth buying.

For: Anyone pricing a market that needs several things to happen in a row.

Turn a poll's subgroup numbers back into a headline figure, weighted by how big each group is.

For: Anyone reading a poll crosstab and wondering what it says overall.

Spotted a mistake or want another calculator? Write to hello@fluxrbot.com or @fluxrbot on X.