Back-Lay Calculator
Find the exact lay stake for any matched betting qualifying bet. Enter your back stake, back odds, lay odds, and exchange commission — the calculator shows the optimal lay stake and your qualifying loss across both outcomes.
What is a qualifying bet?
Before a bookmaker releases your free bet or bonus, they usually require you to place a “qualifying bet” — a real-money stake at minimum odds (typically ≥1.80 or ≥2.00). By laying this bet on the exchange at the same time, you ensure the outcome is the same regardless of the result: a small, controlled qualifying loss.
The qualifying loss is usually 2–5% of your stake when you use odds between 2.00–4.00 with back and lay prices close together. You accept this small cost because the free bet you unlock is worth far more — often 70–80% of its face value when you convert it with the bonus bet converter.
Optimal lay stake = Back stake × Back odds ÷ (Lay odds − Commission). This sizes the lay bet so that your net position is equal whether the back bet wins or loses — the qualifying loss is then just the spread between back and lay odds, multiplied by your stake.
Tips for minimising your qualifying loss
- Use odds between 2.00 and 4.00: Most AU bookmakers accept minimum odds of 1.80 or 2.00 for qualifying bets. At odds of 2.50–3.50 with a tight back/lay spread, qualifying loss is typically 2–4% of stake.
- Match to liquid markets: AFL, NRL, and A-League head-to-head markets on Betfair AU have tight spreads — often just 1–2 ticks between back and lay. Avoid obscure markets where the spread can blow out to 10%+.
- Check both exchanges: Betfair AU and Sportsbet Exchange often have different prices on the same market. The calculator lets you compare — just update the lay odds field.
- Time your lay bet: Exchange prices move. Match your back and lay bets within seconds of each other during business hours when liquidity is highest.
Qualifying loss vs qualifying profit — when does it happen?
In most cases you will see a small qualifying loss — this is normal and expected. The qualifying loss is the price you pay to receive a free bet worth multiples of that loss. Occasionally, when back odds at the bookmaker significantly exceed lay odds on the exchange (an arbitrage situation), the calculator will show a profit on both sides — a qualifying profit. This is rare but happens during bookmaker price boosts or promotions.