Free prediction market calculators and tools
Estimate profit, convert odds, size positions with Kelly, check paired-outcome arbitrage costs, find useful tools and track your forecasts.
Make your next step clearer
Kalshi & Polymarket profit calculator →
Estimate payouts, fees and profit for a purchase or early sale.
Prediction Market Odds Converter →
Convert probability, contract price, decimal odds and American odds. See what a quoted price means before fees.
Prediction Market Arbitrage Calculator →
Compare the cost of matching YES and NO shares with their $1 combined payout. Calculate fees, net margin, ROI and break-even from your own prices.
Kelly Criterion Calculator for Prediction Markets →
Size a Polymarket, Kalshi or HIP-4 position with the Kelly criterion. Enter your probability, the contract price and fees to get a stake in dollars and contracts.
Find the right match →
Match your platform, workflow, budget and preferred interface with projects whose support has been checked.
Prediction Calibration Journal →
Record your forecasts locally, resolve questions and measure your Brier score without an account.
No account required. Calculations run in your browser. Shared calculator links contain the scenario values you choose to share; the calibration journal stays in local browser storage.