Betting math, done properly

Free betting math calculators. Convert odds, find arbitrage across bookmakers and exchanges, remove the vig, size bets with Kelly, price Polymarket shares.

Calculators

Odds converter
American, decimal, fractional, probability and Polymarket price in one view.
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Arbitrage calculator
Surebets across 2–20 outcomes, lay bets and exchange commission. Stakes for equal profit.
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Devig / fair odds
Remove the vig with five methods and compare fair probabilities.
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Commission calculator
Effective odds, break-even and net profit on a betting exchange.
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EV & Kelly
Expected value, edge and Kelly stake against a fair probability.
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Polymarket converter
YES/NO prices in cents to decimal and American odds, plus the spread.
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Polymarket arbitrage
Paste every YES price in a market group and see whether an arbitrage exists.
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Casino bonus ROI
Expected value of a deposit bonus from the wagering requirement, RTP and game contribution.
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Cashout calculator
The odds a cashout offer settles your bet at, the bookmaker's margin against holding, and what a hedge would lock in instead.
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Hedge calculator
How much to bet on the other side of a bet you already hold: equal profit on every outcome, break even on some, or a target profit, with 2-way, 3-way and lay markets.
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What this site does

Every calculator here runs the same tested math. Paste odds in any format, the site converts them through implied probability, and the results update as you type. Every input is stored in the page address, so you can copy a link to a calculation and send it to someone.

The arbitrage solver handles two to twenty outcomes, lay bets on exchanges, and commission charged on net winnings or on turnover. The devig calculator compares five methods side by side so you can see how much the answer depends on the assumption. The EV and Kelly calculator turns a fair probability into a stake.

A note on exchange rates and fees

Commission rates and prediction-market fees change by region, product and tier. The presets are placeholders that you can edit; check the rate in your own account before relying on a result.

Responsible use

These are tools for understanding prices, not tips. Bet only with money you can afford to lose, and if gambling stops being fun, use the help links in the footer.