Enter both prices and the books

Pick the odds format (American, decimal, or fractional), then type the price each bookmaker is offering on the two opposing outcomes — for example +150 at DraftKings on one side and -130 at FanDuel on the other. Add each bookmaker's name so the stake plan tells you exactly where to place each bet.

2

Set your total stake and read the split

Enter the total you want to risk across both books. The calculator shows the arbitrage % (anything under 100% is a sure bet), how much to stake on each outcome, and the guaranteed profit you lock in no matter which side wins. The stake split is sized so both legs return the same amount.

3

Place both legs fast — or move on

If an arb exists, place both bets quickly before either line moves. Watch the marginal-arb warning: an edge under 0.5% can vanish from a single tick, a rounded stake, or a bookmaker limit. Use the 3-Way Arb tab for soccer (Home/Draw/Away) and the Odds Converter to compare prices quoted in different formats.

Convert each price to decimal odds

American +X → 1 + X/100; American −X → 1 + 100/|X|; Fractional a/b → 1 + a/b

Every price is first converted to decimal odds, where a winning $1 bet returns $decimal (stake included). +150 becomes 2.50, -130 becomes 1.769, and 3/2 becomes 2.50. Decimal odds are already in this form.

Arbitrage percentage

Arb% = (1/odds₁ + 1/odds₂) × 100

1/decimal-odds is the implied probability each price assigns to that outcome. Summed across all outcomes and expressed as a percentage, this is the arbitrage %. Below 100% an arb exists; at 100% the market is fair; above 100% the bookmakers' margin (vig) guarantees a long-run loss.

Optimal stake split

stake₁ = total × (1/odds₁) ÷ (1/odds₁ + 1/odds₂); stake₂ = total − stake₁

Stakes are sized in proportion to each outcome's implied probability so that both legs pay back the same amount. Whichever outcome wins, you collect the same return.

Guaranteed profit

profit = total × 100 / Arb% − total; profit% = profit ÷ total × 100

Because every leg returns the same payout (total ÷ sum of implied probabilities), the profit is locked in. A 96% arb on a $1,000 stake returns about $1,041.67, a guaranteed ~$41.67 (≈4.2%).

Arbitrage % (arb %) The sum of every outcome's implied probability, as a percentage. Under 100% means a guaranteed-profit sure bet; the lower the number, the wider the edge.

Implied probability The break-even win rate baked into a price, equal to 1 ÷ decimal odds. Decimal odds of 2.50 imply a 40% probability.

Sure bet (arb) A set of bets across outcomes of one event, placed at different bookmakers, whose prices disagree enough that one stake plan profits no matter the result.

Stake split How the total stake is divided across the outcomes so that each leg returns the same amount — sized in proportion to implied probability.

Vig / overround The bookmaker's built-in margin: the amount all outcomes' implied probabilities add up to above 100%. A positive overround is why most markets are not arbs.

✅

Clear two-way arb

+150 vs -130, $1,000 stake

Outcome 1 odds +150 Outcome 2 odds -130 Total stake 1,000

Decimal: 2.50 and 1.769. Implied probabilities 40.0% + 56.5% = 96.5% (under 100%, so an arb). Stake about $414 on Outcome 1 and $586 on Outcome 2; each leg returns ~$1,036, a guaranteed profit near $36 (≈3.6%) whichever side wins.

⚠️

Marginal arb that fails

+120 vs -119, $1,000 stake

Outcome 1 odds +120 Outcome 2 odds -119 Total stake 1,000

Implied probabilities total ~99.8%, an arb of only ~0.2% (~$2 profit on $1,000). The marginal-arb warning fires: a one-cent line move, a rounded stake, or a bookmaker bet limit can erase the entire edge — and you've now placed bets at two books that may flag your account.

Sports arbitrage — "arbing" or finding "sure bets" — exploits the moments when two bookmakers disagree about a price enough that you can bet every outcome and profit regardless of the result. This calculator converts any odds format to decimal, tells you whether an arb exists, sizes the stake on each side, and shows the guaranteed profit for both two-way and three-way markets.

How the Sports Arbitrage Calculator works

Each price is converted to decimal odds, then to an implied probability (1 ÷ decimal odds). Summing the implied probabilities across all outcomes gives the arbitrage %. When that total is below 100%, the combined market is mispriced in your favor: staking each outcome in proportion to its implied probability makes every leg pay back the same amount, locking in a profit of total × 100 / arb% − total. The further below 100% the arb % sits, the larger the guaranteed edge.

Inputs and what they mean

The odds-format selector controls how every price is read, so set it before typing. Odds fields accept American (+150 / -130), decimal (2.50), or fractional (3/2). The total stake is split for you — you don't enter individual stakes. Bookmaker names are labels only; they appear in the stake plan so you know where to place each leg. The 3-Way Arb tab adds a third outcome for markets like soccer (Home / Draw / Away), and the Odds Converter shows any single price in all formats plus its implied probability.

Limits, edge cases, and a word of caution

Real arbs are usually small and short-lived. Lines move within seconds, so both legs must be placed almost simultaneously; an edge under 0.5% (the marginal-arb warning) rarely survives slippage, rounding, or minimum-stake rules. Bookmakers actively limit or close accounts they suspect of arbing, and stake maximums can prevent you from placing the full recommended amount. Legality varies by country and US state — sports betting is permitted in some jurisdictions and prohibited in others. This tool is for educational and informational purposes only; it is not betting, financial, or legal advice. Never wager more than you can afford to lose, and if gambling stops being fun, seek help (in the US, call or text 1-800-GAMBLER).

What is sports arbitrage betting?+

Sports arbitrage ("arbing" or a "sure bet") means placing bets on every outcome of an event at different bookmakers whose prices disagree enough that one stake plan guarantees a profit regardless of the result. It works because each book sets its own line, and occasionally the combined implied probabilities of opposing prices add up to less than 100%.

How do I find arb bets?+

Compare the same market across several bookmakers and look for opposing prices whose implied probabilities sum to under 100%. Many bettors use odds-comparison sites or dedicated arb-finding software to scan dozens of books in real time. When you spot a candidate, paste both prices into this calculator to confirm the arb % is below 100% and to get the exact stake split before the line moves.

Is arbitrage betting legal?+

Arbitrage betting is not illegal in itself in most places where sports betting is legal, but legality of the underlying betting varies by country and, in the US, by state. Separately, bookmakers' terms of service generally allow them to limit, void, or close accounts they believe are arbing, so the practical risk is account restriction rather than legal trouble. Always check your local laws and each book's terms; this calculator is informational only and not legal advice.

How do I calculate guaranteed profit?+

Convert each price to decimal odds, sum the implied probabilities (1 ÷ decimal odds) to get the arb %, and if it's below 100% the guaranteed profit on a given stake is total × 100 / arb% − total. For example, a 96% arb on $1,000 returns about $1,041.67 — a locked-in ~$41.67 — because the proportional stake split makes every outcome pay back the same amount.

What's different about a three-way arbitrage?+

Three-way markets — common in soccer, where Home, Draw, and Away are all possible — simply add a third outcome. The math is identical: convert all three prices to decimal, sum their implied probabilities, and if the total is under 100% you have an arb. Use the 3-Way Arb tab, which splits your stake across all three books so every result returns the same payout. Three-way arbs are rarer and usually thinner because there are three prices that all have to disagree in your favor.

Sports Arbitrage (Arb) Calculator

Stake & odds format

Two outcomes

Arbitrage result

Guaranteed profit vs. arbitrage %

Three outcomes (e.g. Home / Draw / Away)

3-way arbitrage result

Convert any odds

All formats

How to Use This Calculator

Enter both prices and the books

Set your total stake and read the split

Place both legs fast — or move on

Formula & Methodology

Key Terms Explained

Real-World Examples

Clear two-way arb

Marginal arb that fails

Understanding the Sports Arbitrage (Arb) Calculator

How the Sports Arbitrage Calculator works

Inputs and what they mean

Limits, edge cases, and a word of caution

Frequently Asked Questions

Sports Arbitrage (Arb) Calculator

Stake & odds format

Two outcomes

Arbitrage result

Guaranteed profit vs. arbitrage %

Three outcomes (e.g. Home / Draw / Away)

3-way arbitrage result

Convert any odds

All formats

How to Use This Calculator

Enter both prices and the books

Set your total stake and read the split

Place both legs fast — or move on

Formula & Methodology

Key Terms Explained

Real-World Examples

Understanding the Sports Arbitrage (Arb) Calculator

How the Sports Arbitrage Calculator works

Inputs and what they mean

Limits, edge cases, and a word of caution

Frequently Asked Questions

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