Arbitrage Calculator

Check whether two prices form a guaranteed-profit arbitrage — and get the exact stake split and locked return.

Worked example

Book 1 has Team A at +110 (decimal 2.10); Book 2 has Team B at +105 (2.05). Implied probabilities: 47.6% + 48.8% = 96.4% — under 100%, so it’s an arb. On a $100 total stake you’d put $49.40 on A and $50.60 on B; either result returns $103.74, a locked +3.7%.

How it works

market %  = 1/decimal_A + 1/decimal_B
arb if market % < 100%
stake_A   = total × (1/decimal_A) / market %
stake_B   = total × (1/decimal_B) / market %
profit    = stake_A × decimal_A − total   (same for B)

FAQ

What is sports arbitrage?

Betting every outcome of a market at different sportsbooks so the combined prices guarantee a profit no matter who wins. It works when one book’s price is high enough that the total implied probability across both sides is under 100%.

How do I know if there’s an arb?

Add the implied probabilities of both sides (1 ÷ decimal each). If the total is below 100%, an arbitrage exists — and the amount below 100% is your guaranteed margin.

How do I split my stake?

Stake each side in proportion to its implied probability so both outcomes return the same amount. This calculator does the split for you from your total stake.

Why isn’t arbitrage easy money?

Arbs are small, short-lived, and get you limited or banned fast — books hate arbitrageurs. Lines also move between placing the two bets. Positive-EV betting is usually more sustainable.

Is arbitrage betting legal?

It’s legal in most places, but sportsbooks’ terms let them limit or close accounts that arb. It’s a cat-and-mouse game, not a loophole.

Arbitrage vs. middling — what’s the difference?

Arbitrage locks a small guaranteed profit; middling bets two sides on a moved line hoping BOTH win (a big payout) while risking only the vig. Middles are +EV but not guaranteed.

Educational tool only. Not betting advice. Sportsbooks may limit or close accounts that arbitrage.