Balance a back and lay bet to lock in a near risk-free return.
Qualifiers & SNR free bets
This calculator is an educational tool for understanding how matched betting works mathematically. It does not provide betting advice, tips, or predictions.
Use this matched betting calculator to keep qualifying losses small and lock in profit from stake-not-returned free
bets. Enter the back odds from the bookmaker, the lay odds on the exchange and your commission rate to see the lay
stake, liability and profit for each outcome.
How the calculation works
Core formula (qualifying bet):Lay Stake = (Back Stake × Back Odds) ÷ (Lay Odds − Commission)
Worked example: Back £10 @ 4.0, lay odds 4.2, commission 2% (0.02).
Outcome
Back P/L
Lay P/L
Net
Back wins
+£30.00
−£30.65
−£0.65
Lay wins
−£10.00
+£9.38
−£0.62
Lay stake = (£10 × 4.0) ÷ (4.2 − 0.02) = £9.57.
Always gamble responsibly. This calculator is for information only and does not guarantee profit.
Select qualifying for standard bets, free bet for stake-not-returned offers, or risk-free if the promo refunds as a free bet.
What is free bet retention?
Retention estimates how much of the free bet value you keep after laying it off on the exchange.
Do I need exchange commission?
Yes. Commission affects net profits, so include your rate for more accurate results.
When to use a matched betting calculator
Matched betting uses the mathematics of back and lay bets to extract value from bookmaker promotions. The principle is straightforward: you place a back bet with a bookmaker and an opposing lay bet on an exchange, covering both outcomes. The calculator works out the exact lay stake needed so that the qualifying bet costs as little as possible, and the free bet returns the maximum profit.
This calculator handles two scenarios. For qualifying bets, it minimises your loss by finding the lay stake that balances the back and lay sides as closely as possible. For free bets (where you do not lose your own stake if the bet loses), it maximises your extraction by calculating the optimal lay stake to lock in the highest guaranteed profit.
Detailed worked example
A bookmaker offers "Bet £10 get a £10 free bet." You need to place a qualifying bet first, then use the free bet.
Step 1 — Qualifying bet:
Back £10 at odds of 3.0 with the bookmaker.
Lay the same selection on Betfair at 3.1 with 2% commission.
If the free bet wins: bookmaker pays £40, exchange costs £32.63 → net profit ≈ £7.37.
If the free bet loses: you lose nothing (free bet), exchange pays £7.77 × 0.98 = £7.61 → net profit ≈ £7.61.
Free bet profit: roughly £7.37 to £7.61.
After deducting the qualifying cost, the total profit from this promotion is approximately £6.85 to £7.18.
Common mistakes with matched betting
Choosing the wrong bet type: Qualifying bets and free bets require different calculations. Always select the correct mode in the calculator.
Using odds that are too far apart: A large gap between the back and lay odds increases your qualifying loss. Look for selections where the back and lay prices are close together.
Forgetting "stake not returned" on free bets: Most free bets do not return the stake if the bet wins. If the free bet does return the stake, the calculation changes significantly.
Not accounting for exchange commission: Even small commission percentages affect your lay stake and overall profit. Always enter the correct rate.
Related guides
Matched Betting Guide — a full introduction to matched betting concepts and strategy.
