The short answer
Arbitrage works a disagreement between bookmakers. Two books price the same market differently enough that covering every outcome across them returns more than it costs, for as long as both prices stand.
Matched betting works a promotion. The bookmaker has offered something with a value attached, usually a bonus bet or a refund, and the technique covers the other outcomes elsewhere so that the promotion can be converted into ordinary money.
One is a market inefficiency. The other is a marketing budget. Neither has a certain outcome, and both are described far more confidently elsewhere than either deserves.
How each one actually works
In arbitrage you find a market where the prices across two or more books, taken together, cover every outcome for less than the payout. You stake each outcome in proportion so that the return is the same whichever result lands, and the margin is the difference.
In matched betting you place the bet the promotion requires, then cover the other outcomes at another book so that the result of the event matters as little as possible. The value you are extracting is the promotion itself, not the prices.
The mechanics look the same because both involve backing every outcome across books and sizing the legs so the outcomes balance. The arbitrage calculator on this site does the sizing arithmetic for either.
Where they differ, and why it matters
The differences are practical rather than theoretical, and they decide which one is available to a given person on a given day.
- Source of value: a pricing discrepancy in one case, a promotion in the other. The first is created by the market, the second by the book deliberately.
- Supply: promotions are finite, targeted at particular accounts, and stop arriving once a book decides you are not the customer it wanted. Price discrepancies keep occurring as long as books price independently.
- Frequency: matched betting front loads. New accounts attract sign up offers, and the ongoing supply is much thinner than the opening one.
- Attention: converting promotions is one of the most visible things an account can do, because the book knows exactly who took the offer and what happened next.
- Longevity: both attract restriction. Promotional offers usually stop appearing first, which is why their disappearance is a useful early warning about how an account is being read.
- Skill: matched betting is mostly about reading terms carefully. Arbitrage is mostly about speed and access to enough independent books.
What neither one is
Neither is certain. Both are frequently marketed as though the outcome were settled in advance, and that framing is wrong for the same reasons in both cases.
A leg can be voided or a market resettled, which turns a balanced position into an open one. Prices move between the first leg and the second. Stakes get partially matched or refused. A book can reverse an obvious pricing mistake under its palpable error terms. Accounts get restricted mid method, sometimes with money still in play.
The maths in both cases is sound. The execution is where money is actually lost, and no calculator removes that.
Both also depend on holding funds across several bookmakers at once. That is capital tied up and exposed to the operational reality of the accounts holding it.
Which one applies to you
If your accounts are new and promotions are arriving, the promotional value is usually the larger and simpler thing to work on, and it requires no scanning software to find.
If your accounts are established and the offers have stopped, that avenue narrows considerably, and price differences become the thing still available.
In practice many people do both, because the same accounts and the same arithmetic serve both. The important discipline is to treat neither as a settled outcome, and to read the terms attached to any promotion before assuming it can be converted at all.