Free tool
Arbitrage Calculator
Test whether two opposing prices leave a gap at all, size both legs to the same return — and see what a voided leg or a limited account costs you.
An arbitrage (or "surebet") exists when bookmakers price the same event so that backing every outcome locks in a profit regardless of the result. Enter the best price on each side and your total stake: if the combined implied probability is below 100%, the calculator shows how to divide your stake for an equal, guaranteed return whichever outcome wins.
Odds & stake
Result
- Market % (implied)
- 96.40%
- Stake on A
- 49.40
- Stake on B
- 50.60
- Guaranteed profit
- 3.73
- Return on stake
- 3.73%
How it works
An arbitrage calculator looks at two opposing prices for the same two-way market — for example the two players in a tennis match — and works out whether backing both outcomes guarantees a profit regardless of the result. This is possible when two different bookmakers disagree enough about the odds that their combined prices leave a gap. The tool adds the implied probabilities of both prices to give the combined market percentage. When that total is below 100%, an arbitrage (or "sure bet") exists: the calculator then splits your total stake between the two selections so that each outcome returns the same amount, and reports the guaranteed profit and the return on investment (ROI). Bettors use it to try to lock in a small margin from pricing discrepancies. The edges are usually thin — often 1% to 5% — and they appear and vanish quickly, so the calculator's job is to size the two stakes correctly and confirm the profit before the prices move.
Worked example
Suppose two bookmakers price the two sides of a match at 2.10 and 2.10, and you have £100 to stake in total. Combined market %: (1 / 2.10) + (1 / 2.10) = 0.4762 + 0.4762 = 0.9524 = 95.24% Because 95.24% is below 100%, an arb exists. Stake split (proportional to each price's implied probability): Side A: £100 × 0.4762 / 0.9524 = £50.00 Side B: £100 × 0.4762 / 0.9524 = £50.00 Return whichever side wins: £50 × 2.10 = £105.00 Guaranteed profit: £105.00 − £100.00 = £5.00 ROI: £5.00 / £100.00 = 5.00% Whatever the result, you get back £105 from £100 staked — a £5 locked-in profit.
Arbitrage is not risk-free in practice: bookmakers actively limit, restrict or close accounts that they identify as arbing, and a price can change or a bet be voided before your second leg is placed, leaving you exposed on one side. Always stake both legs as quickly as possible and check each bookmaker's rules on cancelled events and maximum payouts.
Frequently asked questions
What is a sure bet or arbitrage in betting?
It is a situation where two bookmakers price the same two-way market far enough apart that backing both outcomes guarantees a profit. It exists only when the combined implied probability of both prices is below 100%.
How do I calculate the arbitrage stake split?
Divide your total stake by each price in proportion to its implied probability, so both outcomes return the same amount. The calculator does this automatically and shows the stake for each side.
How much profit can arbitrage betting make?
Margins are typically small, often around 1% to 5% per bet, because pricing gaps are minor and short-lived. The 95.24% market in our example returns a 5% ROI, but most real opportunities are tighter.
Is arbitrage betting allowed?
It is legal in most jurisdictions, but bookmakers' terms permit them to limit or close accounts they believe are arbing, and they routinely do so. Treat account restrictions, not the law, as the main practical risk.
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Before you deposit
A calculator can price the bet. It can't price the bookmaker.
Margin, bonus terms, withdrawal limits and the licence behind them differ by operator, and they decide what betting actually costs you — not the number on this page. We publish the same checkable facts for every sportsbook we list: its licence, its responsible-gambling tools, what its bonus terms require and which payment methods it publishes. Check them before you deposit — over time the margin is the certainty, the win is not.