How to Calculate Matched Betting With a Free Bet and an Exchange

Matched betting with a free bet is a way to turn a bookmaker's free bet into cash by placing an opposing lay bet on a betting exchange, which fixes the result whichever way the event goes. For example, a $30 SNR free bet at back odds of 5.00, lay odds of 5.20 and 5% commission locks in $22.14, or 73.79% of face value. Our matched betting calculator finds the lay stake that balances the two outcomes and shows liability and profit. It does not model wagering: the offer's terms decide whether the amount can be withdrawn. The $22.14 assumes the calculated lay is fully matched at 5.20. A lay price 0.30 higher, at 5.50, costs $1.22 of profit.

What matched betting with a free bet is

Matched betting with a free bet combines a bookmaker back bet with a lay on the same outcome at a betting exchange. The calculation aims to make the combined result equal whether the selected outcome wins or loses.

The free bet funds the back bet. If that bet wins, the bookmaker winnings offset the liability lost on the exchange. If it loses, the lay wins, and the exchange winnings after commission provide the result.

The free bet's face value is not the same as the profit it produces. With SNR, meaning stake not returned, only the winnings are paid when the back bet wins. With SR, meaning stake returned, the payout also includes the stake. This distinction determines which calculation applies; it is not a setting to choose according to the result you prefer.

How the lay works: back, lay and liability

A back bet supports an outcome happening; a lay bets against it. Liability is the amount you lose on the betting exchange if the outcome you have laid wins.

The lay stake and liability are different amounts. In the SNR example, the lay stake is $23.30, but the liability is $97.86. If the back bet wins, it is the liability—not the lay stake—that must be deducted from the bookmaker winnings. The exchange account must hold at least that liability: $97.86 in this example. In Full offer mode the calculator shows the largest such figure as “Peak liability”.

If the selected outcome loses, the lay wins. The calculation applies exchange commission to net market winnings, not to the free bet's face value or the liability. This is why commission enters the formula for balancing the outcomes.

Use the lay bet calculator to check the lay stake at a given price. Keep the free bet type in mind: the same face value and odds require different lay stakes for SNR and SR.

In the interface, "Lay stake to place" is the amount of the lay bet, while "Liability" is the possible exchange loss. Neither figure alone is the combined profit from both bets.

The SNR free bet formula step by step

For an SNR free bet, calculate the winnings without returning the stake, then divide those winnings by the lay odds minus commission expressed as a decimal. This gives the lay stake that balances the outcomes under the stated assumptions.

The table lists the values and results of the worked example. Extraction measures profit as a share of the free bet's face value; it is not the payout from a winning back bet.

Diagram of the $30 SNR free bet calculation: lay stake $23.30, liability $97.86, profit $22.14Educational diagram: $30 SNR free bet at back 5.00, lay 5.20 and 5% commission.

Let F be the free bet amount, B the back odds, L the lay odds, c commission as a decimal, and S the lay stake.

SNR free bet winnings = F × (B − 1)
Lay stake S = F × (B − 1) / (L − c)
Liability = S × (L − 1)

Profit if the back bet wins =
SNR free bet winnings − liability

Profit if the lay wins = S × (1 − c)

Apply the formula in this order:

• Calculate the free bet winnings: 30 × (5.00 − 1) = $120. Do not add the SNR stake to this amount.
• Find the lay stake: 120 / (5.20 − 0.05) = $23.30.
• Check the liability: 23.30 × 4.20 = $97.86.
• Compare the outcomes: the calculation gives $22.14 if the back bet wins and $22.14 if the lay wins after commission.

Money amounts are rounded to cents, and extraction to two decimal places. Extraction is taken from the unrounded profit, so dividing the rounded $22.14 by $30 gives 73.80%. This calculation assumes the stated odds, commission and execution of the calculated lay; it does not model changes while placing the bets.

To apply the SNR or SR calculation to your own figures, use the free bet calculator. Select the stake-return type that matches the offer before interpreting its results.

SR free bet: why the result is higher

The SR result is higher because a winning back bet returns the stake as well as the winnings. At the same odds and commission, that changes both the required lay stake and the liability. The SR lay stake is the free bet amount times the back odds, divided by lay odds minus commission: 30 × 5.00 / (5.20 − 0.05) = $29.13.

Both columns use back odds of 5.00, lay odds of 5.20 and 5% commission. The higher SR profit comes with higher liability, so comparing profit alone misses part of the calculation.

An SR calculation describes an offer only when the stake is actually returned. Changing the calculator mode cannot change the bookmaker's payout rules.

Qualifier and full offer

The full offer result is the free bet profit minus any qualifying loss. If a real-money qualifying bet is needed to unlock the free bet, the bonus-stage result alone does not describe the whole offer.

Here, the qualifying bet is $10 at back odds of 2.00, lay odds of 2.04 and 5% commission. Lay stake = 10 × 2.00 / (2.04 − 0.05) = $10.05; liability = 10.05 × 1.04 = $10.45.

The calculator calls the cost of this stage "Qualifying loss". Combining it with the SNR free bet gives:

Free bet profit − qualifying loss = net profit
$22.14 − $0.45 = $21.69

Under these assumptions, the net profit is $21.69, or 72.3% of the free bet's face value. Unlike the free bet-only figure, this includes the cost of the qualifier.

Use the matched betting calculator in "Full offer" mode to calculate both stages together. It separates the free bet profit, qualifying loss and overall net result.

What moves the result: commission and lay odds

Of the market-price changes shown, a lay price 0.30 higher (5.50) matters more than a cut in commission from 5% to 2%: −$1.22 against +$0.57.

Each row changes only the stated assumption relative to the baseline profit of $22.14.

The SR row changes an offer condition rather than a market price. It is included for comparison, not as an alternative available for every free bet.

Under these assumptions, an SNR free bet gives about $22; if the lay goes to 5.50, profit falls below $21; if it is an SR free bet, the result is close to $28. Check the available lay price before placing the bet rather than relying on an earlier calculation.

Wagering requirements: what the calculator does not model

The calculator has no wagering field and does not model turnover. Its result therefore does not establish that withdrawal requirements have been met.

Unibet, ASA case A14-277424, illustrates the distinction. The operator's position described in the ruling was that withdrawing a refunded stake required wagering it 6x: a £10 bonus required £60 in bets. ASA treated the requirement to place further bets at specified odds as a significant condition and found the advertising misleading where that condition was omitted. Full text: ASA ruling A14-277424.

That case does not establish a rule for all free bets. It shows why a balanced betting result and eligibility to withdraw are separate questions. Equal results on both outcomes do not mean the withdrawal conditions are met.

Before betting, establish whether this offer has wagering requirements and which conditions govern withdrawals. If it does, the $22.14 is not withdrawable until those conditions are met. Turnover bets carry their own costs, such as commission and price gaps, which the calculator does not add up. A general guide to wagering, mostly built around casino bonuses, is here: how wagering requirements work.

Limits and mistakes

A risk-free bet is not necessarily free of risk, and a free bet is not cash. Other common mistakes are confusing SNR with SR or assuming that a calculated result is independent of how the lay is executed.

In Petfre, ASA case A13-224692, the refunded amount was returned as a free bet rather than cash that could be withdrawn. ASA considered this a significant condition that should have appeared in the body of the email. See the ASA ruling A13-224692, dated 19 June 2013.

Before calculating and placing the bets, check the operator's terms and confirm:

• Whether a winning free bet returns its stake.
• Whether the back bet and lay refer to the same selected outcome.
• Whether the commission matches your exchange account.
• Whether the calculated lay stake has been matched at the intended odds.
• What form any refund takes and what the operator permits you to withdraw.

The interface label "Guaranteed profit" means the result at these odds and this commission, if the calculated bets are placed as calculated. It is not an unconditional promise or a description of what happens when a lay is only partially matched.

How to calculate in the calculator

Choose "Free bet" for the bonus stage alone, or "Full offer" to include a qualifying bet. Enter the actual offer terms rather than more favourable figures from the example.

For the SNR example:

• Select "Free bet".
• Enter 5 in "Exchange commission (%)".
• Enter 30 in "Free bet amount".
• Select "SNR".
• Enter 5.00 in "Back odds".
• Enter 5.20 in "Lay odds (exchange)".
• In "Result", check "Lay stake to place", "Liability" and "Guaranteed profit". The example values are $23.30, $97.86 and $22.14.

To include the qualifier, select "Full offer". For the qualifying bet, enter 10 in "Qualifying stake", 2.00 in "Back odds" and 2.04 in "Lay odds (exchange)". Keep commission at 5% and enter the SNR free bet values above for the free bet stage.

Compare "Free bet profit", "Qualifying loss" and "Net guaranteed profit" with the example's $22.14, $0.45 and $21.69 respectively. If your figures differ, run the calculation again rather than treating these example figures as targets.