Arbitrage Betting Calculator
Split a stake across every outcome, round it so it looks natural, add exchange commission, work out lay bets and free bets, and re-hedge when the odds move before your second bet. Trading on prediction markets? Use the Kalshi arbitrage calculator.
Arbitrage Calculator
Without rounding, stakes are rounded to whole cents. Exact stakes like $494.27 are a red flag to sportsbooks. Rounding makes your bets look normal; the result shows what it costs you.
| Outcome | Odds | Stake | Payout | Profit if it wins |
|---|
Back & Lay Calculator
Exchanges always show decimal odds, so the lay odds field stays decimal in both formats. Typical commission: Betfair about 5%, Smarkets about 2%.
| If the outcome… | Sportsbook | Exchange | Net |
|---|
Odds Moved Calculator
Do not re-split the total stake. The first bet is fixed; only the second stake changes. The first bet is assumed to be at a sportsbook with no commission.
How the math works
Is there an arbitrage?
Turn each decimal odd into an implied probability (1 divided by the odds) and add them up. If the total is below 100%, the odds from different sportsbooks disagree enough to lock in a profit. At 2.10 and 2.05 the total is 47.6% + 48.8% = 96.4%, so the margin is about 3.6%.
Rounding
Rounded stakes no longer pay exactly the same on every outcome. The calculator shows the profit for each outcome and the worst case, so you can see whether rounding still leaves a profit.
Exchange commission
An exchange takes commission from your net winnings, which lowers the odds you really get.
Lay bets and free bets
Laying an outcome on an exchange covers every result except that one, so one back bet plus one lay bet can lock in a result. A free bet does not return its stake when it wins, so its lay stake is smaller.
When the odds move
If the second leg's odds change after your first bet is placed, size the second bet so both outcomes pay the same as the first bet would.
American odds
Positive odds: divide by 100 and add 1 (+150 becomes 2.50). Negative odds: divide 100 by the number and add 1 (−120 becomes 1.83).
Finding arbs by hand is slow. A scanner checks 100+ bookmakers for you and fills in this calculator.
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For educational purposes only. This is not financial advice. Results assume every bet is accepted at the odds you entered. Odds move fast, so confirm them at each sportsbook before you place a bet. Many sportsbooks restrict arbitrage in their terms. Gamble only where it is legal for you, and only with money you can afford to lose.