By Michael ·
Arbitrage betting means backing every outcome of an event at prices whose implied chances add up to under 100%, so each result pays a little. Matched betting is different: it accepts a small, known loss on purpose to get a bookmaker offer, and the value comes from the offer.
How an arb works
Every price has an implied chance: 1 divided by the decimal odds. At one bookmaker the implied chances for all outcomes add up to more than 100%. The extra is the bookmaker's margin. Our guide to betting odds explained shows how that works.
An arb appears when you take the top price for each outcome from different places and the total drops below 100%.
Example: a made-up tennis match between Player A and Player B. Bookmaker One offers Player A at 2.10, an implied chance of 47.6%. Bookmaker Two offers Player B at 2.05, which is 48.8%. Together that's 96.4%.
Split £100 in line with those chances: £49.40 on Player A and £50.60 on Player B. If Player A wins, you get £103.74 back. If Player B wins, you get £103.73. That's about £3.73 on £100 staked, if both bets are accepted at those prices and both stand.
Prices can move before you place both bets, and then the gap is gone.
Football is harder. A match result market has three outcomes, so a bookmaker-only arb needs three bets, all accepted at the right price. That's three chances for a price cut, a stake limited to a few pounds, or a postponed match settled differently at each site. It's one reason matched bettors cover a football bet with a single lay at an exchange. One lay covers the draw and the away win together.
The back and lay arb
A back bet is a normal bet that something will happen. A lay bet, placed at a betting exchange, is a bet that it won't. Matched bettors meet arbs as a bookmaker's back price that's higher than the exchange's lay price, once commission is counted.
Example: a bookmaker offers the home side at 3.20 and the exchange lay is 3.10, with 2% commission. You back £20.
The lay stake is £20.78 and the liability is £43.64. The liability is what you pay the exchange if the home side wins. In that case you're up £44.00 at the bookmaker and down £43.64 at the exchange, so 36p up. If the home side doesn't win, you lose the £20 back stake and the exchange pays £20.36 after commission. That's 36p up again.
The match rating, which compares the back price with the lay price after commission, is 101.82%. Anything above 100% is an arb. Our guide to lay betting explained shows where the lay stake comes from.
Now change only the commission. At 5%, the same prices leave you about 7p down whichever way it goes. Thin arbs live or die on commission, so use your own rate, not a guess.
What's different in matched betting
In matched betting you usually expect to lose a little on each bet. Example: back £20 at 3.00 and lay at 3.10 with 2% commission, and you're 91p down whatever happens. That's the qualifying loss. You accept it because the bet gets you something: a free bet, a 2UP early payout or an extra place in a horse race.
Point | Arbing | Matched betting |
|---|---|---|
Where the value comes from | A gap between two prices | A bookmaker offer |
Usual result per bet | A small gain on paper | A small known loss, plus the offer |
Needs a promotion | No | Yes |
Main risk | A bet voided, resettled or cut | A missed lay or a wrong stake |
The two overlap. A back and lay arb is a matched bet where the prices happen to favour you. Our alert pages show a rating for each match, and above 100% means the back price beats the lay. Check it again with your own commission, and treat it as a bonus, not a plan. Our guide to what is matched betting covers the offers side.
What goes wrong with arbs
An arb only works if every bet stands at the price you saw.
The price can move before your second bet. You back at 3.20, then find the lay has moved from 3.10 to 3.40. Now you're about £1.44 down either way, not 36p up. Check the second price is still there before you place the first.
The bookmaker can void the bet. The Bet365 terms say that if it believes you've been arbing, it can void the bets, hold back the winnings and close the account. If the £20 back is voided, you're left holding only the lay. You win £20.36 if the home side doesn't win and lose £43.64 if it does. A tiny arb has become a large open bet.
A price the bookmaker calls an obvious error is a separate rule. The Bet365 terms say those bets stand but are settled at its corrected price. Example: if the 3.20 is corrected to 2.80, a home win now pays £36.00 against the £43.64 liability, so you're £7.64 down on that result.
The bet can be cut. You ask for £50 and the bookmaker accepts £8. Your other side is now far too big.
The sites can settle differently. Before you back both sides, read how each site settles an abandoned match or a tennis player retiring. If the rules differ, one bet can be made void while the other loses.
Your account can be restricted. The Bet365 terms say it may close, limit or suspend your account at any time. If that account gave you offers, you've lost more than the arb was worth. Our guide to account restrictions explains the different kinds.
Betting exchanges make their money from commission.
Is arbing legal in the UK?
Yes. No UK law stops you backing different outcomes at different bookmakers. But Bet365's terms say it may close, limit or suspend an account at any time. They also list arbing as a prohibited activity, and describe it as using differences in odds between sportsbooks, or betting on every outcome of an event. Legal and welcome are two different things.
When not to bother
If the arb is under about 1% after commission, one price move or a rounded stake can wipe it out. And if the bookmaker is one you use for offers, an arb that gets you noticed can cost you those offers. Many matched bettors skip pure arbs and stick to the offers. Results vary either way, and a missed step costs money in both.
Questions people ask
Can an arb still lose money?
Yes. A price move, a voided bet, a cut stake or a different settlement rule can each turn an arb into a loss.
How do bookmakers spot arbers?
Bookmakers don't publish how they decide. The Bet365 terms do say what they count as arbing, as above.
Do I need software to arb?
You need the stakes worked out. The sum below tells you whether the pair is an arb.
Check the numbers before you bet
Multiply the back odds by 1 minus your commission. For 3.20 at 2%, that's 3.20 × 0.98 = 3.136.
Take your commission off the lay odds. For 3.10 at 2%, that's 3.10 less 0.02 = 3.08.
If the first number is bigger, the prices are an arb at that moment. Here 3.136 beats 3.08, so it is.
Put the same prices into the 2UP Calculator for the lay stake and liability.
Check the money waiting at your lay price and the bookmaker's terms before you decide whether it's worth it.
Checked against Bet365's terms on 14 November 2026.
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