Arbitrage betting explained: how arbs work and how to calculate the stakes

An arbitrage (an arb or a sure bet) happens when two or more bookmakers price the same event so differently that backing every outcome, at the right stakes, returns the same amount whichever way it goes, and that amount is more than you staked. This post shows how to spot one, how to split the stake, and why arbs are harder to collect than the arithmetic suggests. The free arbitrage calculator does the sums for you.

The test: do the implied probabilities add up to less than 100%?

Take the best available price for each outcome, from whichever book offers it, and add up 1 / odds:

• Book A: Player 1 at 2.12, so 1 / 2.12 = 47.17%
• Book B: Player 2 at 2.05, so 1 / 2.05 = 48.78%
• Total: 95.95%

Below 100% means an arbitrage exists. The gap is your return: 1 / 0.9595 - 1 = 4.22% on the total stake.

If the total is 100% or more, there is no arb: any split of the stake loses at least the margin.

The stake formula

To make every outcome pay the same, stake each one in proportion to its implied probability:

stake_i = total_stake × (1 / odds_i) / S, where S is the sum of the implied probabilities.

With 100 to stake on the example above:

Either result returns 104.22: a profit of 4.22 on 100.

Three-way markets

The same formula works for 1X2 soccer markets. Say the best prices across three books are 2.30 / 3.60 / 4.20:

• 1/2.30 + 1/3.60 + 1/4.20 = 43.48% + 27.78% + 23.81% = 95.07%
• Return: 1 / 0.9507 - 1 = 5.19%

Stakes for 100: 45.74 on home, 29.22 on the draw and 25.05 on away. Each returns about 105.19.

Three-way arbs are rarer, because three books have to be wrong at the same time.

Why arbs exist at all

Most bookmakers do not set their own prices from scratch. They follow a sharp market, and the market they watch most is Pinnacle. When Pinnacle moves on new information and a slower book has not followed yet, the two prices can briefly cross. That gap is the arb, and it closes as soon as the slow book updates.

That is why speed matters so much. Arbitrage scanners compare many books at once, and the sharp side of the gap is usually the Pinnacle price that just moved. The Pinnacle odds dropper shows how often and how far those moves happen, and the WebSocket API pushes each change as it happens.

The risks the formula hides

• Prices move before you finish. If one leg's price changes before you place it, the arb can turn into a loss. Place the leg most likely to move first.
• Voids and rule differences. Books settle some events differently (for example a tennis retirement, or whether extra time counts). Check that every leg settles the same way.
• Limits and account restrictions. Many soft books cut stakes on accounts that take arbs. Your real capacity is often much lower than the advertised maximum.
• Rounding. Odd stake amounts can draw attention, and rounding them changes the return slightly. The calculator shows the exact figures so you can see the effect.
• Palpable errors. A price that looks too good may be voided by the book as an obvious mistake.

Arbs vs value betting

An arb locks in a small certain return per event but is hard to scale. Value betting takes only the side priced above the fair price (see how to calculate no-vig odds) and accepts variance in exchange for more volume. Many bettors use the same sharp reference price for both.

PinnRadar provides odds data, not betting advice. Check the rules and terms of every bookmaker you use.