Matched bettors back a bet with the bookmaker and lay the same selection on an exchange to lock in a profit whatever happens, and they live and die by this distinction. Because an SNR free bet only pays winnings, the stake has to come out of the calculation. In practice that means using back odds − 1 rather than the full back odds when you work out the lay stake.
SNR lay stake = (Free bet × (Back odds − 1)) / (Lay odds − Commission)
For a cash qualifying bet, or a Stake Returned free bet, you use the full back odds instead:
Lay stake = (Back stake × Back odds) / (Lay odds − Commission)
Commission goes in as a decimal, so 2% is 0.02.
Take a £10 SNR free bet backed at 5.0 and laid at 5.2 on an exchange charging 2%. The lay stake works out at £10 × 4.0 / (5.2 − 0.02) = £7.72, which carries a liability of £32.42. If the back bet wins you collect £40, pay out the liability and bank £7.58. If the lay wins you keep the £7.72 less commission, a £7.57 profit. Either way, that's roughly 76% of the free bet's face value locked in.
It's why matched bettors hunt for SNR free bets at higher odds where the back and lay prices sit close together. Our betting promotions guide goes further on turning offers into profit, and bookmakers versus betting exchanges explains the lay side.
