What is a lay stake?
Lay stake: The lay stake is the amount you stake AGAINST a selection at the exchange: what you keep if the selection doesn't happen, before commission.
When you place a lay bet at Smarkets, Betfair Exchange or Matchbook, the exchange shows two prominent numbers: the lay stake and the liability. Beginners almost always read the lay stake and stop there. That's where most early matched-betting errors come from.
The lay stake is the amount of money you stand to win if the lay bet wins (that is, if the selection doesn't happen). It's the headline figure on the exchange's bet slip. The liability, by contrast, is calculated as lay_stake × (lay_odds − 1) and is the figure the exchange holds back from your balance until the event settles. The two numbers are different sizes by design, and on most matched-betting odds the liability is roughly twice the lay stake.
Our standard matched betting calculator does the lay-stake calculation automatically once you enter the back odds, lay odds, back stake, and exchange commission rate. The output it gives you is what to type into the exchange's bet slip. From there, the calculator's expected qualifying loss should match what actually happens to within a few pence.
Worked example
You're qualifying for a £10 free bet by placing a £10 back at 3.0 odds at Bet365. Plug those numbers into the calculator with Smarkets' lay odds at 3.10 and 2% commission, and the calculator returns a lay stake of £6.45.
That £6.45 is what you put in the "Backer's stake" box on Smarkets' bet slip. The site then shows the liability as roughly £13.55. That's 6.45 × (3.10 − 1), the amount Smarkets holds in escrow against your balance until the match ends. Same exchange bet, two completely different numbers, and only one of them is what you actually paid in.
Common mistake
Sizing your exchange bankroll based on lay stake alone, then being surprised the bet won't go through. The exchange shows the lay stake on the front of the bet slip, but it can only accept the bet if your balance covers the liability, usually 2–3× the lay stake at typical matched-betting odds. Rule of thumb: keep at least three times your typical lay stake's liability available at the exchange, and read the exchange liquidity guide before going for larger qualifiers.