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DefiRate calculators: what they do, what they cost, where they stop
Last checked 2026-09-08
DefiRate publishes 13 free browser calculators for prediction market trades, covering odds conversion, expected value, fee impact, arbitrage, Kelly sizing, hedging, parlays and a Monte Carlo bankroll simulator. The page lists 11 supported platforms, from Polymarket and Kalshi to Robinhood, ForecastEx and Coinbase.
It suits a trader who wants one page for pre-trade math and does not want to maintain their own sheet. It is an advertising-supported reference, not a data feed, so every number you type in is yours to source.
What it does
The suite is a set of independent single-purpose calculators on one page. Each takes a few inputs (price in cents, stake, fee rate, your probability) and returns the result instantly in the browser.
The Platform Fee Reference and Fee Impact Analyzer are the two that differ from a generic betting calculator: they carry per-venue fee assumptions, so the output changes when you switch from Kalshi to Robinhood.
- Odds Calculator: converts between contract cents, American, decimal and fractional odds
- Expected Value Calculator: expected profit per bet from price and your probability
- Platform Fee Reference and Fee Impact Analyzer: fee tables and profit after fees at different trade sizes
- Arbitrage Finder and Multi-Market Comparison: the same market priced across platforms
- Kelly Criterion, Position P&L, Hedging, Break-Even Probability, Vig/Overround, Parlay/Multi
- Bankroll Simulator: Monte Carlo trajectories of a bankroll under a given edge and stake
Pricing
Every calculator is free with no account. DefiRate describes itself as independent and advertising-supported, so the page carries ads and venue promotions around the tools.
Venues and data
The supported-platform list at the time of checking was Polymarket, Kalshi, Robinhood, PredictIt, Crypto.com, ForecastEx, OG.com, FanDuel, DraftKings, Coinbase and Gemini.
The fee reference states Polymarket US at a 0.10% taker fee, Kalshi at 0.07% to 1.75% on a formula, and Robinhood at a flat $0.02 per contract. Fee schedules change; treat these as DefiRate's snapshot and check the venue before sizing a trade on them.
Where it falls short
Nothing is live. The Arbitrage Finder and Multi-Market Comparison compare prices you enter by hand; they do not pull order books, so they cannot tell you a spread exists, only whether the one you found clears fees.
The Kelly and bankroll tools assume your probability estimate is right. They size a bet; they do not improve the forecast behind it.
It finds the spread on paper. Executing it means opening Kalshi and Polymarket separately, or a cross-venue terminal.
Who should use it
A discretionary trader placing a handful of positions a week who wants fee-aware EV and hedge numbers in seconds. A systematic trader will outgrow it quickly, because none of the outputs can be called from code.
Questions about DefiRate calculators
Are the DefiRate prediction market calculators free?
Yes. All 13 calculators run in the browser with no account or payment. The site is supported by advertising.
Does DefiRate's calculator work with Kalshi fees?
Yes. The fee reference and fee impact tools carry a Kalshi entry at 0.07% to 1.75% on a formula, alongside 10 other platforms including Polymarket, Robinhood and ForecastEx.
Does the DefiRate arbitrage finder scan live markets?
No. You enter the prices from each venue yourself and it tells you whether the pair is profitable after fees. It does not pull live order books.
What does the DefiRate bankroll simulator do?
It runs a Monte Carlo simulation of bankroll paths from your stake, edge and number of bets, so you can see the range of outcomes rather than a single expected value.
Trackers find the edge. Calculators size it. Alerts time it.
When it is time to execute, the free Kairos terminal trades Kalshi, Polymarket and Predict.fun from one book.