Betting mathematics
Matched Betting Calculator: Back, Lay & Liability
Enter the back stake, back and lay prices, and your exchange commission to compare both outcomes. This calculator models one fully matched back/lay pair, not a guaranteed profit.
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Qualifying bet and bonus-bet formulas
For a cash stake S, back odds B, lay odds L and commission fraction c, equalizing the two outcomes gives lay stake = S × B ÷ (L − c). For a bonus bet whose face-value stake is not returned, use S × (B − 1) ÷ (L − c). The tool rounds the lay stake to cents and then calculates both outcomes again.
Lay liability = lay stake × (L − 1). If the selection wins, the back profit is S × (B − 1), less the lay liability. If it loses, the lay winnings after commission are lay stake × (1 − c), less the cash back stake; for a stake-not-returned bonus there is no cash back stake to subtract.
Worked example with commission
With a $100 cash stake, back odds 3.00, lay odds 3.10 and commission 2%, the rounded lay stake is $97.40 and liability is $204.54. The net results are −$4.54 if the selection wins and −$4.548 before display rounding if it loses. Selecting the bonus mode changes the required lay stake because the face-value stake is not paid back.
Commission is entered by you, not taken from a live account. The model applies it to the winning lay side of this isolated pair. Other positions in the same market, discounts or different commission rules can change the actual charge.
What matched betting does not guarantee
Prices must refer to the same outcome and settlement rules. Partial fills, unavailable liquidity, voids, deductions, account limits, qualification rules and bonus restrictions can change the result. Taxes, wagering requirements and offer eligibility are not evaluated. Never treat the model as confirmation that a promotion is available or that both bets have been accepted.
For two ordinary back bets, use the arbitrage and dutching calculator; for a fixed existing ticket, use the hedge stake calculator.
Compare an underlay or overlay
Select Custom lay stake to model a different amount at the entered lay price. A smaller lay stake leaves more exposure to the selection losing; a larger stake increases liability if it wins. With $100 backed at 3.00, $50 laid at 3.10 and 2% commission, liability is $105. Net is $95 if the selection wins or −$51 if it loses.
Custom mode models one fully matched lay position. It does not assume an unfilled order will execute, combine partial fills at different prices or model a refund promotion. Compare both net results, including any negative result. Cash and stake-not-returned bonus modes use different deductions; a refund paid as bonus credit is not the same as a cash refund.
Methodology and references
For the underlying terminology, see Betfair explanation of lay stakes and liability. This independent calculator uses the assumptions explained above; check your operator’s current settlement terms. The reference is not an endorsement or an account integration.