Back and lay odds → the lay stake that levels both outcomes, your liability, and what you're left with either way.
Bet type
Your back stake is returned if the bet wins, so the aim is to make the loss either way as small as possible.
The two outcomes are levelled deliberately, so whichever side wins you end up in the same place.
About this calculator
Matched betting works by backing a selection with a bookmaker and laying the same selection on an exchange, so that one bet covers the other. The lay stake is chosen so your net position is identical whichever way the event goes — that is what "locking in" means.
For a qualifying bet, where the bookmaker returns your stake if it wins, the lay stake is (back odds × back stake) ÷ (lay odds − commission). The small difference between the back and lay prices means you normally end up slightly down — that shortfall is the qualifying loss, and it is the cost of unlocking a free bet.
For a stake-not-returned free bet, the bookmaker pays only the winnings, so the lay stake is (back odds − 1) × back stake, divided by (lay odds − commission). Because you are not risking your own money on the back side, the levelled figure is a genuine profit — typically around 70–80% of the free bet's face value, depending on how close the two prices are.
Liability is what the exchange holds from your balance while the lay bet is open: lay stake × (lay odds − 1). Commission is applied to net winnings on the exchange side only, which is the standard model at UK exchanges. This tool assumes a stake-not-returned free bet in free bet mode, no partial matching, and that both bets are placed at the prices you enter.
Frequently asked questions
Why do I lose a small amount on a qualifying bet?
Because the lay price at the exchange is almost always a little higher than the back price at the bookmaker, and commission is charged on top. That gap is the qualifying loss — usually a small, predictable cost that you accept in order to unlock a free bet worth much more.
How much of a free bet can I actually keep?
Typically around 70–80% of its face value. The closer the back and lay odds are, the more you retain, which is why free bets are usually placed at higher odds where the proportional gap between the two prices is smaller.
What is liability and why is it bigger than my lay stake?
Liability is what you would pay out if the selection wins, calculated as lay stake × (lay odds − 1). You need that amount available in your exchange account for the bet to be matched, so it is the real cash requirement rather than the lay stake itself.