Arbitrage Betting, Explained.
An arbitrage — a "sure bet" — is when prices on the same market disagree enough that you can back every outcome and profit whoever wins. It happens because bookmakers price independently: when their views drift apart, the combined market can briefly imply less than 100% probability. This guide covers the maths (with a worked example), exchange commission, the real-world risks, and how TACTIX's Arbitrage Finder does the work for you.
The Idea in One Formula
Every price implies a probability: implied % = 1 ÷ decimal odds
Add up the best implied probability for each outcome of a market. If the total is under 100%, the bookmakers have collectively over-priced the market — you can cover every outcome and lock a profit of (1 ÷ total) − 1
Normally the opposite is true: a single bookmaker's 1X2 market adds up to more than 100%. That excess is the overround — the bookmaker's built-in margin, typically a few percent. An arb only appears when you combine the best price from different operators and the overround flips negative.
A Worked Example
Suppose the best available prices on a match, each at a different bookmaker, are:
| Outcome | Best odds | Implied probability | Stake share |
|---|---|---|---|
| Home win | 2.10 | 47.62% | £48.00 |
| Draw | 3.60 | 27.78% | £28.00 |
| Away win | 4.20 | 23.81% | £24.00 |
| Total | — | 99.21% | £100.00 |
The implied probabilities sum to 99.21%, so this is an arb with a locked margin of (1 ÷ 0.9921) − 1 = 0.80%. Splitting £100 in proportion to each 1/odds means every outcome returns roughly £100.80 — a profit of about 80p whichever way the match goes. Small, which is typical: most genuine arbs are under 1%, because operators correct big gaps fast.
Three Kinds of Arb
Exchange commission matters more than it looks: a 2% commission on the lay side of a 1% arb can wipe out the entire edge. Any honest arb calculation nets commission out before declaring a margin — TACTIX's Arbitrage Finder does this on every number it shows, and its stake calculator splits your money so each outcome returns the same amount after commission.
How to Check an Arb, Step by Step
- Find the best price on every outcome — across different bookmakers, or a bookmaker and an exchange.
- Convert each price to an implied probability — 1 ÷ decimal odds. A price of 2.10 implies 47.6%.
- Add them up — below 100% is an arb; 100% or above is not.
- Net out exchange commission — reduce any lay leg's effective return by the commission rate before judging the edge.
- Split your stake in proportion to 1/odds — so every outcome returns the same amount. The margin is (1 ÷ total) − 1.
- Place all legs quickly and re-check prices — an arb only exists if every leg is matched at the calculated price.
The Risks (It's Not Free Money)
Prices move while you're placing the legs — the second leg of a two-leg arb can vanish mid-execution, leaving you with a plain single bet you never wanted. Bookmaker stake limits and thin exchange liquidity can stop you matching the full amount. Bets can be voided or palped (cancelled as a palpable error) on one side only, which converts your "sure bet" into an open position. And bookmakers routinely restrict or close accounts that arb consistently — exchanges generally don't, which is one reason back/lay arbs are popular.
The honest summary: the profit is mathematical, the execution is not. Treat quoted arb margins as a ceiling, not a promise, and never stake money you can't afford to have stuck in a half-completed position.
Frequently Asked Questions
What is arbitrage betting?
Arbitrage betting (an "arb" or "sure bet") means staking on every outcome of a market at prices high enough that the combined implied probability is under 100% — so you lock in a profit whichever result occurs. It exists when different bookmakers (or a bookmaker and a betting exchange) disagree enough on the odds.
How is an arbitrage calculated?
Add up 1/odds for the best price on each outcome. If the total is below 1, it's an arb: the profit margin is (1 / total − 1). You then split your stake in proportion to 1/odds so every outcome returns the same amount. For a bookmaker-versus-exchange arb you also subtract the exchange's commission from the lay side.
Is arbitrage betting risk-free?
No. Prices move between placing the legs, stake limits and exchange liquidity can stop you completing both sides, bets can be voided or palped, and bookmakers may restrict accounts that arb consistently. The profit is mathematical, not guaranteed in practice. 18+, gamble responsibly.
How big is a typical arbitrage margin?
Most genuine arbs are small — commonly under 1% and rarely more than a few percent — because bookmakers build a margin (the overround) into every market and correct big pricing gaps quickly. Larger apparent arbs are often stale prices or errors that will be voided, which is itself a risk.
Is arbitrage betting legal in the UK?
Placing arbitrage bets is not illegal in the UK — you are simply taking the prices operators offer. However, bookmakers' terms allow them to limit stakes or restrict accounts, and they routinely do so to consistent arbers. Betting exchanges generally do not restrict winners, which is why many arbs pair a bookmaker back with an exchange lay.
How does TACTIX find arbitrage opportunities?
TACTIX's Arbitrage Finder continuously compares the odds it tracks across bookmakers and exchanges on the same markets, nets exchange commission out of every calculation, and shows the resulting margin with a stake-split calculator. TACTIX is an analytics service — it surfaces the numbers; it does not place bets or handle money.