Matched BetsHow to calculate a lay stake
Short answer
For a cash (qualifying) bet, lay stake = back stake × back odds ÷ (lay odds − commission), with commission written as a decimal (2% = 0.02). A £10 back bet at 3.0, laid at 3.1 with 2% commission, needs a £9.74 lay. Free bets and refunds use slightly different formulas, below.
The terms
- Back stake (S) and back odds (B): your bet at the bookmaker, in decimal odds.
- Lay odds (L): the price you lay at on the exchange.
- Commission (c): the exchange's cut of winning lay bets, as a decimal.
- Liability: what you pay the exchange if your lay loses, equal to lay stake × (L − 1).
The aim is a lay stake that makes the result the same whether the back bet or the lay bet wins.
Qualifying bet (cash stake)
Example: S = £10, B = 3.0, L = 3.1, c = 0.02. Lay stake = 30 ÷ 3.08 = £9.74 (rounded to the penny). Liability = 9.74 × 2.1 = £20.45.
| Outcome | Bookmaker | Exchange | Result |
|---|---|---|---|
| Back wins | +£20.00 | −£20.45 | −£0.45 |
| Lay wins | −£10.00 | +£9.55 | −£0.45 |
The exchange pays 9.74 × (1 − 0.02) = £9.55 when the lay wins, because commission comes off lay winnings.
Free bet, stake not returned (SNR)
The bookmaker pays winnings only, so there is no stake to lose and none to get back:
Example: a £10 SNR free bet at 3.0, laid at 3.1: 20 ÷ 3.08 = £6.49. Result: +£6.37 if the back wins, +£6.36 if the lay wins.
Free bet, stake returned (SR)
The payout includes the stake, so the whole return is hedged — the same lay as a qualifying bet, but with no stake at risk:
Example: £10 SR at 3.0, laid at 3.1: £9.74, locking in +£9.55 either way.
Refund offers
With a "money back as a free bet if you lose" offer, the expected value of the refund (award × conversion rate) is part of the losing side. If you expect to convert a £10 free bet at 80%, treat it as £8:
Example: £10 at 3.0, laid at 3.1, £10 refund at 80%: (30 − 8) ÷ 3.08 = £7.14. If the back wins you make £5.01 cash. If the lay wins you're −£3.00 in cash plus a free bet worth about £8.00 — £5.00 once you use it. The refund is an estimate, not cash, which is why Matched Bets reports it separately. More on strategy and conversion rates in refund offers.
Underlay and overlay
You don't have to balance both outcomes. With the qualifying example above:
| Strategy | Lay stake | If back wins | If lay wins |
|---|---|---|---|
| Standard (balanced) | £9.74 | −£0.45 | −£0.45 |
| Underlay | £9.52 | +£0.01 | −£0.67 |
| Overlay | £10.20 | −£1.42 | £0.00 |
Underlaying moves the result towards the back winning; overlaying towards the lay winning. They're mainly used for refund offers and promotions that pay out on one outcome. Always compare both results before you bet.
Partial matches
If the exchange only matches part of your lay, or you lay in pieces at different odds, each piece has its own liability. Work out what is already covered and lay only the remainder:
Example: £5 already matched at 3.05 on the qualifying bet above. That fill has £10.25 liability, so the remaining lay at 3.1 is (30 − 10.25 − 4.90) ÷ 3.08 = £4.82, with a total liability of £20.37 and about −£0.37 either way. See partial lay matches for what to do when the price moves.
Rounding
Exchanges accept stakes in pennies or cents. Round the lay stake to two decimal places, then work out the outcomes from the rounded stake — that's why the two results can differ by a penny.
Common mistakes
- Using fractional odds in the formula. Convert 5/2 to 3.5 first (decimal = 1 + 5 ÷ 2).
- Forgetting commission, or using the wrong rate for your exchange.
- Using the qualifying formula for an SNR free bet — it lays too much.
- Not checking the liability fits your exchange balance before placing the lay.
Run your own numbers in the free matched betting calculator, which handles every case above, including partial matches.