Matched betting
Back/lay calculator
Backing a selection at a bookmaker and laying the same selection at an exchange leaves you with the same result whichever way the event goes. This calculator finds the lay stake that equalises the two outcomes, the liability you need available at the exchange, and what the position actually settles at.
Exchange commission is charged on the net winnings of the lay bet, so the equalising denominator is the lay price minus the commission rate. Getting that wrong is not a rounding difference: it flips the sign of the answer at ordinary commission rates, and it makes a higher-commission exchange look more profitable than a cheaper one.
Inputs
Most free bets are stake-not-returned: the winnings are paid without the stake.
Charged on net winnings. Typically 2% but varies by exchange and by market.
Leave at 100% to equalise. Below 100% underlays, leaving upside if the back bet wins.
Result
- Lay stake
- €9.65
- Liability at the exchangeMoney that must be available in the exchange account
- €40.53
- If the bookmaker selection wins
- -€0.53
- If the exchange selection wins
- -€0.54
- Qualifying loss
- -€0.54
Assumes both bets are matched at the prices shown. Exchange liquidity, price movement between placing the two legs, and bookmaker stake limits all change the real result. Bookmakers may also restrict accounts.
How this is calculated
lay stake = (S x B) / (L - c) [free bet, stake not returned: (S x (B - 1)) / (L - c)]
S is the back stake, B the back price, L the lay price and c the commission rate as a fraction. Commission is charged on the lay bet's net winnings, so it reduces the effective lay price by exactly c — hence the denominator L - c. A common error is to use L - (L - 1) x c, which is the formula for expressing a lay as an equivalent back price, not for sizing the stake. At a EUR 10 stake, 5.00 back, 5.20 lay and 5% commission that error returns a lay stake of 10.02 and reports a small profit, when the correct stake is 9.71 and the position is a loss of about EUR 0.78.
Worked example
A qualifying bet placed to unlock a promotion, laid off at an exchange charging 5% commission.
- 01Back EUR 10 at 5.00 with the bookmaker. If it wins you receive EUR 50, a EUR 40 profit.
- 02The exchange offers 5.20 to lay, with 5% commission. The equalising denominator is 5.20 - 0.05 = 5.15.
- 03Lay stake = (10 x 5.00) / 5.15 = EUR 9.71. Liability = 9.71 x 4.20 = EUR 40.79.
- 04If the selection wins: +EUR 40 at the bookmaker, -EUR 40.79 liability = -EUR 0.79.
- 05If it loses: the lay pays 9.71 less 5% commission = EUR 9.22, against the EUR 10 back stake = -EUR 0.78.
- 06Either way the qualifying bet costs about EUR 0.78 — the price of unlocking the promotion.
Questions
Why is the qualifying loss bigger when commission is higher?
Because commission is a cost. It reduces what the lay bet pays you when it wins, so it can only ever make the position worse. If a calculator shows profit improving as commission rises, its commission model is wrong.
What is the difference between a stake-returned and stake-not-returned free bet?
A stake-not-returned free bet pays only the winnings — a EUR 10 bet at 5.00 returns EUR 40, not EUR 50. Stake-returned free bets pay the full return and are worth substantially more, which is why the two need different lay stakes.
What does the lay proportion do?
Setting it below 100% underlays: you lay less than the equalising amount, so you keep some upside if the bookmaker selection wins and take a larger loss if it does not. The calculator recomputes both outcomes from the adjusted stake, so the figures shown are the real ones rather than the balanced-lay figures.
Why is my liability rounded up?
Liability is money that has to be sitting in your exchange account. Rounding it down would tell you that you need less than you actually do, and the bet would be rejected.
Related calculators
These calculators are information tools. They describe the arithmetic of the prices you enter — they are not advice, and they do not predict outcomes. Betting involves risk. 18+ only. If gambling is causing you harm, support is available from Peluuri.