Back Lay Calculator
Enter the bet you place at the bookmaker and the lay price on the exchange, and the calculator gives the lay stake that makes both outcomes pay the same, the liability you need in your exchange account, and the result if the selection wins or loses. It handles qualifying bets and free bets, both stake not returned (SNR) and stake returned (SR), with exchange commission.
The formula in one line: lay stake = back stake × back odds ÷ (lay odds − commission). £10 at 3.00, laid at 3.10 with 2% commission: 10 × 3.00 ÷ 3.08 = £9.74, liability £20.45, result −45p whichever side wins. For a SNR free bet, use back odds − 1 in place of back odds.
Fractional prices? Convert them with the odds converter first. Commission is charged on net winnings of the lay and varies by exchange and market; check the figure your exchange shows on the bet slip.
Result
If the selection wins
If the selection loses
How the Lay Stake Is Worked Out
Backing means betting that something happens; laying, on a betting exchange, means taking the other side and acting as the bookmaker. Hold both bets on the same selection and one of them always wins. The only question is the lay stake that leaves you with the same amount whichever one it is.
Write the two outcomes down and set them equal. If the selection wins, the bookmaker pays back stake × (back odds − 1) and the exchange takes lay stake × (lay odds − 1). If it loses, you lose the back stake and the exchange pays the lay stake less commission. Solving for the lay stake gives back stake × back odds ÷ (lay odds − commission). The worked example from the box above:
- £10 backed at 3.00, laid at 3.10, commission 2% (0.02).
- Lay stake: 10 × 3.00 ÷ (3.10 − 0.02) = 30 ÷ 3.08 = £9.74.
- Liability: 9.74 × 2.10 = £20.45, held by the exchange until the result.
- Selection wins: +£20.00 at the bookmaker, −£20.45 on the exchange = −£0.45.
- Selection loses: −£10.00 at the bookmaker, +£9.74 × 0.98 = +£9.55 on the exchange = −£0.45.
What the gap between back and lay prices costs
The same £10 qualifying bet at 3.00 with 2% commission, laid at different prices. The further the lay price drifts from the back price, the more the qualifying bet costs:
| Lay odds | Lay stake | Liability | Result either way |
|---|---|---|---|
| 3.00 | £10.07 | £20.13 | −£0.13 |
| 3.05 | £9.90 | £20.30 | −£0.30 |
| 3.10 | £9.74 | £20.45 | −£0.45 |
| 3.20 | £9.43 | £20.75 | −£0.75 |
| 3.40 | £8.88 | £21.30 | −£1.30 |
Even with identical prices the bet loses 13p, because commission is taken from the lay winnings. That is the floor on any qualifying bet.
Free bets: why SNR changes the formula
Most UK free bets are stake not returned: a winning £10 free bet at 5.00 pays £40, not £50. Because there is no stake to lose and no stake to get back, the lay stake uses back odds − 1: 10 × 4.00 ÷ (5.20 − 0.02) = £7.72, liability £32.43. The selection wins: +£40.00 − £32.43 = £7.57. It loses: £7.72 × 0.98 = £7.57. You keep 75.7% of the free bet's face value whatever happens.
Higher prices keep more of the value in theory, as long as the back and lay prices stay close; a wide gap at long odds wipes the gain out. With a £10 SNR free bet at 5.00 and 2% commission, a lay at 5.10 keeps £7.72, at 5.50 £7.15 and at 6.00 £6.56. The free bet calculator shows what a free bet returns on its own, without a lay, and the guide to free bets and deposit bonuses explains the terms that decide whether an offer is worth taking.
Underlaying and overlaying
A lay stake below the calculated one (an underlay) shifts money towards the outcome where the selection wins; a larger one (an overlay) shifts it towards a loss. On the £10 qualifying bet above, laying £8.00 instead of £9.74 gives +£3.20 if the selection wins and −£2.16 if it loses; laying £11.00 gives −£3.10 and +£0.78. Either choice turns a fixed cost into a bet on the result, which is the opposite of what the calculator is for.
Each-way and horse racing
An each-way bet is two bets, so it needs two lays: one on the win market and one on the place market, each with its own price and stake. Use the each-way matched betting calculator for those. A Rule 4 deduction at the bookmaker is not applied the same way on the exchange, where a reduction factor is used instead, so a non-runner can leave the two sides slightly out of balance; the Rule 4 guide shows how the bookmaker side is settled.
Frequently Asked Questions
How do you work out a lay stake?
For a normal bet, lay stake = back stake × back odds ÷ (lay odds − commission), with commission written as a decimal. £10 backed at 3.00 and laid at 3.10 with 2% commission needs a lay stake of 10 × 3.00 ÷ 3.08 = £9.74. That stake makes the result the same whichever side wins: a loss of 45p either way.
What is lay liability?
Liability is what you pay out on the exchange if the selection wins, and it has to be in your exchange account before the lay is matched. It equals lay stake × (lay odds − 1). A £9.74 lay at 3.10 carries a liability of £20.45, more than twice the back stake, which is why the exchange balance needed is usually larger than the bet itself.
What is the difference between a free bet SNR and SR lay?
SNR means stake not returned: a £10 free bet at 5.00 pays £40 profit and the £10 is not given back, so the lay stake uses back odds − 1: 10 × 4 ÷ (5.20 − 0.02) = £7.72. SR means stake returned, as with a cash bet, so the full back odds are used: 10 × 5 ÷ 5.18 = £9.65. Most UK free bets are SNR.
Why does a qualifying bet lose a little money?
The lay price is almost always higher than the back price, and the exchange takes commission on lay winnings. Both gaps cost money. The qualifying loss is the price of unlocking the free bet; on a SNR free bet the calculator shows how much of the free bet's face value you keep, typically 70% to 80% when the back and lay prices are close.
Is matched betting legal in the UK?
Yes. Betting and laying the same selection breaks no law, and exchange winnings are not taxed for UK residents. Bookmakers are free to limit or close accounts they consider bonus-led, and their terms decide whether an offer applies. The calculator works out the arithmetic only; it does not check whether a bet qualifies for a promotion.
A lay bet can cost far more than the back stake: the liability is the real amount at risk on the exchange. A wrong price or a lay left unmatched turns a covered bet into an open one. 18+. Set limits before you start and, if gambling stops being fun, see our responsible gambling resources.