What Is Arbitrage Betting & How Do You Lock In a Margin?
Arbitrage betting (“arbing”) means backing every outcome of an event across different bookmakers — or backing and laying on an exchange — at prices whose combined implied probability is under 100%, so you lock in a small profit whatever the result. It is maths and speed rather than luck, and UK bookmakers can limit accounts that do it.
🔑 Key takeaways
- An arb exists when the combined implied probabilities of all outcomes total under 100%.
- Most arbs are small (around 1–3%) and rely on both bets being matched before the odds move.
- You usually pair a fixed-odds bookmaker with a betting exchange and pay commission on the exchange.
- Arbing is legal in the UK, but bookmakers can restrict or close accounts that do it regularly.
📑 On this page
Arbitrage betting is a strategy that takes advantage of differences in the odds offered by different bookmakers. When prices do not line up correctly, it can be possible to back every outcome and secure a small margin no matter what happens. It is often called “arbing”, and in reality it is less about gambling instinct and more about maths and timing.
The profits per bet are usually small, but the aim is to remove as much uncertainty as possible. That only works if everything is placed correctly — and quickly.
What is arbitrage betting?
Arbitrage betting is a method where you back two (or more) opposing outcomes to lock in a guaranteed margin. Typically you pair a traditional bookmaker with a betting exchange that lets you lay odds as well as back them.
With a lay bet you are offering odds on a selection not to win — effectively taking the bookmaker’s role. By finding favourable back and lay prices, you can structure your stakes so the return is balanced across every outcome.
A worked example (with numbers)
In a Wimbledon match, Player A is priced at 1.90 with one bookmaker. A second bookmaker takes a different view and prices the same player at 2.30. Backing each outcome at the best available price can push the combined book under 100%.
The implied probability of 2.30 is 43.48%. Two outcomes at 43.48% total 86.96% — comfortably under 100%, so a theoretical arbitrage exists. You then split your stakes to balance the return.
How to use an arbitrage calculator
A calculator tells you exactly how to divide your stakes. You enter the back odds, the lay odds and the exchange commission, and it returns your stakes and the locked margin. Here is a back-and-lay example on Liverpool v West Ham:
- Back (fixed odds): Liverpool to win at 2.40 — stake £46.01.
- Lay (exchange): Liverpool not to win at 2.10, with 5% commission — stake £53.99.
- Locked profit if both are matched: about £10.42.
The calculator assumes both legs are matched at the listed prices. If the odds move before your second bet is matched, the margin can disappear — which is the single biggest practical risk of arbing.
Arbitrage vs matched betting
You can apply the same back-and-lay maths to matched betting, where you use a bookmaker’s free bet offer instead of two sets of live odds. You place a qualifying real-money bet, receive a free bet, then lay it off on an exchange to extract most of its value. Done correctly this reduces reliance on chance, though it still depends on accurate staking and following each promotion’s terms.
The risks and downsides
Arbing removes most of the variance from a bet and the profit is mathematically defined, which is the appeal. The catches are real, though: bookmakers limit or close accounts they believe are arbing, the margins are small so you need a sizeable bankroll, and prices move fast, so a leg can go unmatched and leave you exposed. If you are chasing value in a more conventional way, our guide to best odds guaranteed bookmakers is a gentler place to start.
Frequently asked questions
Is arbitrage betting legal in the UK? +
Yes, arbing is legal. However, a bookmaker's terms allow them to limit your stakes or close your account if they believe you are arbing, so the risk is practical rather than legal.
Do you pay tax on arbitrage profits? +
No. Gambling winnings — including arbing and matched-betting profits — are tax-free for UK players. Tax is paid by operators, not bettors.
How much money do you need to arb? +
Because the margins are small, most arbers spread a bankroll of several hundred to a few thousand pounds across multiple accounts to make the returns worthwhile.