Matched betting is a risk-minimising technique that turns bookmaker promotions — primarily free bets and welcome bonuses — into near-certain profit. It works by combining a back bet at the bookmaker (where the free bet or bonus is offered) with a lay bet on a betting exchange (such as Betfair) at the same odds, so that the two bets cancel each other out regardless of the result.
The process has two stages. First, a qualifying bet: you place a real-money back bet on a selection at the bookmaker and lay the same selection on an exchange. The back and lay odds are close but not identical (the difference is the qualifying loss), and completing this step triggers the free bet promotion.
Second, a free bet conversion: you use the free bet on a high-odds selection at the bookmaker and lay the same selection on the exchange. Because the free bet stake is not returned (it is a "stake not returned" or SNR free bet), you adjust the lay stake accordingly. The profit extracted from an SNR free bet is approximately 75-80% of its face value, locked in regardless of the outcome.
Ongoing matched betting beyond welcome offers focuses on reload promotions, enhanced odds offers, acca insurance, and cashback deals. Each bookmaker has a different promotional calendar, and dedicated matched betting services track all available offers across dozens of bookmakers.
Example
Bookmaker offers: bet £10, get £10 free bet. You bet £10 on Chelsea at 2.50, then lay Chelsea at 2.52 on Betfair for a qualifying loss of around £0.30. You receive a £10 free bet. You place the £10 free bet on a selection at 6.0, lay it on Betfair at 6.2. Profit: approximately £7.80 from the free bet, minus the £0.30 qualifying loss = ~£7.50 net profit regardless of results.