Free Arbitrage Calculator

How to Use This Calculator

1. Pick your format. Decimal (2.10), American (+110, -200), or Fractional (11/10). Toggle once and every odds field respects the choice.
2. Enter the best price for each side. For 2-way arbs (e.g. moneyline, Yes/No), shop across books or venues for the highest odds on each outcome. For 3-way (e.g. soccer home/draw/away), add the third price.
3. Set the total stake. Enter the total dollars you want to risk across all legs combined. Leave blank to default to $100.
4. Read the result. If the arb percentage is positive, the stake split below it is the exact amount to bet on each side. Place all legs before prices move.

How Arbitrage Math Works

Every set of odds implies a probability. For decimal odds, that implied probability is simply 1 divided by the odds. Add the implied probabilities for all outcomes of a market, and a fair market without margin would sum to exactly 100%. Bookmakers build a margin (juice) into their prices, which is why the sum is usually above 100%.

An arbitrage exists when, because one book is too high on Side A while a different book is too high on Side B, the combined implied probabilities drop below 100%:

Arb % = 100% - (1/OddsA + 1/OddsB) × 100%

To lock in equal profit on either outcome, stake each side in proportion to its implied probability. The formulas for a 2-way arb with a total stake of S are:

StakeA = S × (1/OddsA) / (1/OddsA + 1/OddsB)
StakeB = S × (1/OddsB) / (1/OddsA + 1/OddsB)

Whichever side wins, the payout is the same, because StakeA × OddsA equals StakeB × OddsB.

Worked Example

Sportsbook 1 has Team A at 2.10 decimal (+110 American). Sportsbook 2 has Team B at 2.05 decimal (+105 American). You want to risk $100 total.

• Implied probability A = 1/2.10 = 47.62%
• Implied probability B = 1/2.05 = 48.78%
• Sum = 96.40%
• Arbitrage edge = 100% - 96.40% = 3.60%
• Stake on A = $100 × 0.4762 / 0.9640 = $49.38
• Stake on B = $100 × 0.4878 / 0.9640 = $50.62
• Payout if A wins = $49.38 × 2.10 = $103.73
• Payout if B wins = $50.62 × 2.05 = $103.77

Either way, you collect about $103.73 on a $100 outlay. The guaranteed profit is roughly $3.73, or a 3.73% ROI. Convert any format via the odds converter if your book quotes American or fractional.

2-Way vs 3-Way Arbitrage

A 2-way arb covers markets with exactly two possible outcomes: moneylines in basketball and tennis, Yes/No on a prediction market, Over/Under totals, or player props that resolve binary. Most retail arbs are 2-way because there are fewer prices to coordinate, execution is faster, and pricing is easier to compare.

A 3-way arb covers markets with three outcomes, most commonly soccer match results (home win, draw, away win). The math extends naturally: add 1/OddsC to the implied probability sum, and split the stake across three sides. The downside is that you need three favorable prices at the same moment, and you need to place three bets before any leg moves. This is why 3-way arbs on soccer are usually smaller in percentage but appear more often across European books.

Either way, the engine is identical. Compute the implied probability sum. If it's under 100%, you have an arb. Split the stake in proportion to each side's implied probability.

From Calculator to Automated Execution

Every arbitrage calculator on the internet does the same math. What it cannot do is beat the market to the click. By the time you spot a 3% edge, copy the odds into a form, read the stake split, switch to Sportsbook 1, log in, place the first leg, switch to Sportsbook 2, and place the second leg, the price on one side has usually moved. You end up with a naked single-sided bet and no arb.

That latency gap is the reason most manual arbers give up after a few months. The edges are real, but capturing them requires executing both legs in the same sub-second window, across accounts that are already funded, logged in, and ready to fire.

Claw Arbs solves the timing problem with a background process that streams order books from Kalshi, Polymarket, Pinnacle (PS3838), and BetInAsia, runs the same arbitrage math this calculator runs, and fires both legs in roughly 20 milliseconds when a profitable edge appears. The calculator is useful for verifying opportunities you found manually, sizing a specific trade, or learning the math. For consistent live captures across thousands of markets, automated detection and execution is the only approach that works.

For a comparison of tools in this category, see our best arbitrage betting software breakdown, or the Claw Arbs homepage for feature details.

Frequently Asked Questions

What is an arbitrage calculator?

An arbitrage calculator is a tool that checks whether two or three sets of odds on opposing outcomes add up to less than 100% of implied probability. When they do, it splits your total stake across each outcome so the payout is equal no matter which side wins, producing a guaranteed profit. Input the odds for each side, the total stake you want to risk, and the tool returns the individual stake per outcome, the arbitrage percentage, and the locked-in return.

How do you calculate arbitrage percentage?

Convert each odds to its implied probability by dividing 1 by the decimal odds, then add them together. If the sum is below 1.00 (100%), you have an arbitrage opportunity. The arbitrage percentage is 100% minus that sum, expressed as a percent. For example, decimal odds of 2.10 and 2.05 give 1/2.10 + 1/2.05 = 0.476 + 0.488 = 0.964, which means the edge is 3.6%. That edge, minus fees and slippage, is your locked-in ROI.

What is a good arbitrage percentage?

Anything above 0% before fees is technically an arb, but realistic targets depend on where you bet. On mainstream sportsbooks, edges of 0.5% to 2% are common and still profitable at scale. Prediction markets like Kalshi and Polymarket frequently show edges of 2% to 8% because liquidity and pricing are less efficient. Anything above 5% should be treated with suspicion: verify the odds are live, the market has depth, and no rule (like voided-bet clauses) will break the arb.

Can you lose money on an arbitrage bet?

A correctly executed arb with both legs filled at the quoted odds cannot lose. But real-world risks exist: one leg fills and the other moves before you click, a bookmaker voids the bet, your account gets limited or stake-capped, currency conversion or withdrawal fees eat the edge, or a rule difference (like push rules on Asian handicaps) causes an asymmetric settlement. The only reliable way to avoid these is to execute both legs in the same sub-second window, which is what automated bots do.

Why use an automated arbitrage bot instead of a calculator?

A calculator tells you whether an arb exists right now. An automated bot does the same math across thousands of markets every second, then places both orders the moment an edge appears. By the time a human plugs numbers into a calculator and switches tabs to two sportsbooks, the price on one side has usually moved. Claw Arbs detects cross-venue arbitrage across Kalshi, Polymarket, Pinnacle, and BetInAsia in roughly 20 milliseconds and fires both legs together, so the guaranteed profit is actually locked in.

Related Tools & Reading

• Hedge bet calculator: lock in profit on an existing open bet.
• Parlay and SGP calculator: build accumulators and round robins.
• Odds converter: switch between decimal, American, fractional, and implied probability.
• How to find arbitrage bets: a walk-through on spotting edges across books.
• What is sports arbitrage betting: the full primer on sure bets.
• Live arbitrage scanner: watch real cross-venue arbs and value bets stream in as our engine detects them.