What is arbitrage betting?

Arbitrage betting (an 'arb' or 'sure bet') means backing every possible outcome of an event at different bookmakers whose odds disagree enough that the combined implied probability is below 100%. Because the stakes are split so every result returns the same amount, you lock in a small profit whichever way the event goes.

How do I know if two odds are an arbitrage?

Add the implied probabilities: 1 divided by each set of decimal odds. If the total is less than 1 (100%), it is an arbitrage. For example 2.05 and 2.10 give 1/2.05 + 1/2.10 = 0.488 + 0.476 = 0.964, or 96.4% — under 100%, so about a 3.7% arb.

Is arbitrage betting worth it?

In practice it is hard. Sure bets are small (typically 1-3%), appear briefly and need large stakes to matter, odds move before you place both legs, and bookmakers quickly limit or close accounts they suspect of arbing. It is legal, but it is not free money and it is not sustainable at most books.

Arbitrage betting (sure bets) explained — and the honest catch

Last updated: 2026-07-14 · Gamblerfy editorial team

An "arb" or sure bet sounds like the holy grail: a bet that wins no matter what happens. It's real maths, not a scam — but the version sold in ads ("guaranteed profit!") hides why almost nobody makes a living from it. Here's exactly how it works, and the honest reasons it's far harder than it looks.

What arbitrage actually is

Every price is a probability in disguise: decimal odds of 2.00 imply a 50% chance (1 ÷ 2.00). A single bookmaker builds a margin in, so its own prices on an event add up to more than 100% — that's their edge. Arbitrage happens when two bookmakers disagree enough that, by taking the best price for each outcome from different books, the combined implied probability drops below 100%. Split your stakes correctly and every result pays back the same amount — more than you staked.

A worked example

A tennis match, two players. You find:

Book A: Player 1 at 2.05 → implied 1 ÷ 2.05 = 0.488 (48.8%)
Book B: Player 2 at 2.10 → implied 1 ÷ 2.10 = 0.476 (47.6%)

Total implied probability = 0.488 + 0.476 = 0.964 (96.4%). Under 100%, so it's an arb of about 3.7%. To lock it in on a £100 total, split the stakes in proportion to each implied probability:

Player 1: £100 × (0.488 ÷ 0.964) = £50.60 → returns 50.60 × 2.05 = £103.70
Player 2: £100 × (0.476 ÷ 0.964) = £49.40 → returns 49.40 × 2.10 = £103.70

Either result returns ~£103.70 on £100 staked — a guaranteed ~£3.70 (3.7%), whoever wins.

The honest catch

The maths is real; making money from it is not easy:

Margins are tiny. Real arbs are usually 1–3%, so you need large stakes on both sides for a meaningful return.
They vanish fast. Odds move constantly. By the time you place the second leg, the price can shift and the arb is gone — or turns into a loss.
Bookmakers fight it. Arbing is legal, but books spot the pattern quickly and limit or close accounts they suspect of it. Some also void bets under "palpable error" or bonus-abuse terms.
Execution risk. A rejected bet, a lower "bet accepted" price, or a limit on one side leaves you exposed on the other — the opposite of a sure bet.

"Sure bet" services that charge a subscription rarely account for account limits, moving lines and execution risk — treat "guaranteed profit" claims with heavy skepticism. Bet within a fixed budget for entertainment, not income. Read our responsible gambling guide.

Arbitrage vs value betting

Arbitrage locks a small profit with no view on who wins. Value betting is the opposite bet: you take a single price you think is longer than the true odds, accept the variance, and profit only over many bets. Value scales and is what winning bettors actually do; arbitrage doesn't scale because books shut it down. Both, tellingly, get you restricted once a book decides you have an edge. Our Arbitrage (Sure Bet) Calculator checks any two odds for an arb and splits the stakes for you, and the Odds Converter and Margin & Fair Odds calculator do the rest of the arithmetic.

Come across a term you don't know? Our betting & bonus glossary defines them all in plain English.

Related guides

Bookmaker margin (vig) — why a single book's prices add up to over 100%.
Value betting & expected value — the edge that actually scales.
How betting odds work — reading price as implied probability.
Why betting odds move — why an arb disappears before you place both legs.
Why betting sites limit accounts — what happens to arbers and value bettors.
Betting exchange explained — backing and laying the same outcome.