Arbitrage Betting Calculator

Frequently Asked Questions

What is an arbitrage (sure) bet?

It is when prices across operators let you cover every outcome for a combined implied probability below 100%, theoretically guaranteeing a small profit. This is informational only and not betting advice.

How is an arbitrage detected?

Sum the inverse of the best decimal odds for each outcome (1/odds). If the total is under 1.00 an arb exists; the gap below 1.00 is the rough guaranteed margin.

How are stakes split for an arb?

Each outcome's stake = total bankroll × (1/its odds) ÷ (sum of 1/odds), so every result returns the same amount. The tool computes this split and the locked profit.

Why is real-world arbitrage difficult?

Odds move fast, limits and account restrictions apply, and small margins are eaten by fees and timing. It is rarely as risk-free as the math suggests - treat this as educational.

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This calculator is for informational and educational purposes only and is not betting, gambling, or financial advice. It does not predict outcomes or guarantee returns. Gambling involves risk; never wager more than you can afford to lose. You are responsible for complying with the gambling laws in your jurisdiction.

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How This Calculator Works

This tool is informational and educational only, is not betting advice, and assumes you gamble responsibly. Arbitrage (a "sure bet" or "arb") occurs when two books price the two sides of the same event so generously that backing both sides in the right proportion guarantees a profit no matter the result. It exists because different books disagree on probabilities or move lines at different speeds - one book may post a stale number while another has already reacted to news, a sharp steam move, or a key injury. The window is usually brief because other participants and the books themselves correct the discrepancy quickly. This calculator tests whether the combined implied probability across the two prices is below 100% and, if so, splits a fixed total stake so that the return is identical whichever side wins, then reports the guaranteed profit and ROI. The size of any real arbitrage is almost always tiny - a few percent at most - and it shrinks further once you account for the practical frictions described below, which is why "sure bets" are far less sure in practice than the arithmetic suggests.

Formula / Method

Convert both prices to decimal, D₀ and D₊. The arbitrage percentage = (1 ÷ D₀ + 1 ÷ D₊) × 100. If it is below 100% an arbitrage exists; the gap is the locked margin. For a total bankroll T, stake on side A = T × (1÷D₀) ÷ (1÷D₀ + 1÷D₊), and the remainder goes on side B. Each side then returns the same amount; guaranteed profit = that common return − T, and ROI = profit ÷ T. If the percentage is at or above 100% there is no risk−free profit - the calculator says so honestly.

Worked Example

Book A prices side 1 at +110 (decimal 2.10); Book B prices side 2 at +105 (decimal 2.05). Arb % = (1÷2.10 + 1÷2.05) × 100 = (0.4762 + 0.4878) × 100 = 96.40% - below 100%, so an arb exists. With a 1000 total: stake A = 1000 × 0.4762 ÷ 0.9640 ≈ 493.9; stake B ≈ 506.1. Payout A = 493.9 × 2.10 ≈ 1037.2; payout B = 506.1 × 2.05 ≈ 1037.5. Guaranteed profit ≈ 37 on 1000, an ROI near 3.7% locked regardless of outcome. Now contrast a market with no arb: if both sides were priced −110 (decimal 1.909), arb % = (0.5238 + 0.5238) × 100 = 104.8%, comfortably above 100%, so any stake split loses the overround - there is simply no risk−free profit to extract, and the calculator reports that honestly rather than inventing one. The closer the arb % sits to 100%, the thinner the edge and the more a single rounding error, a half−point line move, or a rejected bet can flip the "sure" profit into a real loss.

Common Mistakes

Acting on stale odds - lines move fast and the arb often vanishes before both bets land.

Ignoring bet limits, account restrictions, and voided bets, which can leave one leg unmatched.

Rounding stakes carelessly so the two sides no longer return equal amounts.

Forgetting fees, currency spreads, or withdrawal costs that erase a thin margin.

Assuming books tolerate arbitrage; many limit or close accounts that do it systematically.

Tips & FAQ

Is arbitrage risk−free? Only in theory - execution risk, line movement, limits, and account closures are real and frequently eliminate the edge in practice. By the time the second bet is placed the first line may have moved, leaving you exposed on one side rather than hedged. Why are arbs usually tiny? Markets are efficient; gaps of a few percent are quickly arbitraged away by others, and the books actively monitor for the betting patterns that arbitrage creates. What does ≥100% mean? No sure bet exists at those prices - the combined book has positive margin and any split forfeits the overround. Will books let me keep doing this? Many limit stakes, void bets, or close accounts of consistent arbitrageurs, so a strategy that looks risk−free on paper often has a short shelf life. Treat any number here as a planning estimate, not a guarantee; betting markets carry structural edges against participants, and even "sure bets" can fail operationally. Wager only what you can afford to lose, set limits in advance, never chase a missed leg with a larger unhedged bet, and seek help if betting stops being entertainment.

Arbitrage Betting Calculator

Frequently Asked Questions

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