Market Math: what it does, what it costs, where it stops

What it does

The home page lists 15 tools in three groups. The prediction market group is the one that is hard to find elsewhere: a market converter, break-even, a PM EV calculator, a multi-outcome calculator, a liquidity calculator and a position risk (correlation) calculator.

The fee page covers Kalshi, Polymarket, Robinhood Event Contracts, DraftKings Predictions, ForecastEx (Interactive Brokers), FanDuel Predicts, PredictIt and Coinbase Prediction Markets, each with worked examples.

• Cross-platform: EV Calculator, De-Vig Calculator, Arb Calculator, Prediction Market Fee Calculator
• Prediction markets: Market Converter, Break-Even, PM EV, Multi-Outcome, Liquidity, Position Risk
• Sports: Odds Converter, Kelly Criterion, Parlay, Hold, Edge
• Publishers can embed the calculators free from /for-publishers

Pricing

The site states the tools are 100% free, with no account required and no usage limits. No paid tier is advertised.

Venues and data

The fee table is the venue coverage: eight platforms. The calculators themselves are venue-agnostic once you pick a fee rate. No live prices are pulled; you enter them.

The site does not name its operator on the pages we fetched, and fee data is not stamped with a last-updated date on the home page, so verify a rate against the venue before relying on it.

Where it falls short

The Arb Calculator tells you whether two prices you already found clear the fees. It does not scan for them. It finds the spread only after you have; executing it means opening the two venues separately, or a cross-venue terminal.

Sportsbook tools share the page with prediction market tools, so a Kalshi-only trader has to skip past de-vig and parlay math that does not apply.

Who should use it

A trader who moves between venues and wants the fee comparison in one place, plus a multi-outcome and liquidity calculator that the single-venue sites do not offer.