Free sports betting calculators
The math behind the Arbs board, free and without an account. Every tool understands Polymarket prices in cents and the Polymarket taker fee as well as American and decimal odds.
- Polymarket odds converter: Convert a Polymarket price in cents to American, decimal and fractional odds and implied probability, before and after the taker fee.
- No-vig calculator: Remove the vig from a two-way or three-way line. See each side’s fair probability and fair odds, and how much margin the book is charging.
- Polymarket fee calculator: Work out the Polymarket taker fee on any sports trade, the total cost, the payout, and the win probability you need to break even.
- Arbitrage calculator: Check whether two or three prices across Polymarket and sportsbooks lock a profit after fees, and how much to stake on each side.
- EV calculator: Enter the odds and your win probability, or a fair line, to see the expected value of a bet per $100 and the win rate it needs to break even.
- Kelly calculator: Size a bet with the Kelly criterion: full, half and quarter Kelly stakes, plus a simulation of how your bankroll could move over 100 bets.
- Parlay calculator: Combine up to 10 legs into one price and payout. Add each leg’s fair probability to see the parlay’s true chance and how much vig it carries.
- Hedge calculator: Holding a bet that has moved your way? See the stake on the other side that locks the same profit either way, or the stake that just gets your money back.
Learn the math
- How to read Polymarket sports odds
- Polymarket vs sportsbooks: fees, limits and settlement
- Polymarket fees explained for sports bettors
- What are no-vig fair odds and how to calculate them
- Arbitrage betting between Polymarket and sportsbooks
- Expected value betting, with worked examples
- Kelly criterion and bankroll sizing for sports bets
- Are parlays ever +EV? Correlation explained
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