By Michael ·
Back bets and lay bets in plain English
A back bet is the bet everyone knows. You pick the home side to win, the bookmaker takes your £10, and you get paid if the home side wins.
A lay bet turns that round. You're saying the home side won't win. If the match ends in a draw or an away win, you win. If the home side wins, you lose. So one lay covers both the draw and the away win.
To lay, you use a betting exchange such as Betfair, Smarkets or Matchbook, where people bet against each other instead of against the house. When you lay, you're matched with someone who wants to back. Their stake becomes what you can win, and what they can win becomes your risk.
That's the core of matched betting: back at the bookmaker, lay at the exchange, and the result matters much less to your balance.
Lay bet liability: the number that catches people out
When you lay, the exchange asks for a stake. That stake is the backer's stake. It's the amount you win if the selection loses, and it isn't what you risk.
What you risk is the liability. That's what you'd pay the backer if the selection wins. Work it out as lay stake × (lay odds − 1).
Example: here's what a £10 lay costs you to cover at three prices.
Lay stake | Lay odds | Liability |
|---|---|---|
£10 | 1.50 | £5.00 |
£10 | 3.00 | £20.00 |
£10 | 11.00 | £100.00 |
It's the same £10 lay stake, with twenty times the money at risk. Laying a favourite is cheap to cover. Laying an outsider ties up a lot of cash, even though you're betting it won't win. If you're new to decimal prices, our guide to betting odds explained shows how 11.00 relates to 10/1.
If the selection doesn't win, you keep the backer's stake. The exchange then takes commission on your net winnings in that market. If you lose on a market, you pay none. Smarkets charges 2% on its standard tier, and Matchbook charges 2% to UK customers. Betfair's rate depends on your My Betfair Rewards package, and the Basic package is 2%.
So a £10 lay that wins at 2% commission pays you £9.80.
How matched bettors use the lay
In matched betting, you lay to cover a back bet you've placed at a bookmaker to get an offer.
Example: you back the home side for £10 at 2.50 at a bookmaker. The exchange lay price is 2.56 and your commission is 2%. The lay stake that makes both results the same is (back odds × back stake) ÷ (lay odds − commission).
That gives a lay stake of £9.84 and a liability of £15.35. If the home side wins, you're up £15.00 at the bookmaker and down £15.35 at the exchange, so you're 35p down. If the home side draws or loses, you lose £10.00 at the bookmaker and win £9.65 at the exchange after commission. That's 35p down again.
That small, known cost is the qualifying loss. It's what you pay to be in place for the offer, whether that's a free bet, a 2UP early payout or an extra place. Most offers end in a small qualifying loss like this one, and results vary.
Notice the lay stake (£9.84) isn't the back stake (£10). It comes from both prices and the commission. Our 2UP Calculator works out the lay stake and liability for you, so you don't have to run the formula by hand.
Why laying the same stake goes wrong
A common first mistake is to lay the same amount you backed. It feels tidy, but you're no longer level.
Example: with the same prices, lay £10 instead of £9.84. If the home side wins, you're up £15.00 and down £15.60, so you lose 60p. If it doesn't, you lose £10.00 and win £9.80, so you lose 20p.
On a £10 bet the gap is small, but on bigger stakes and longer odds it grows quickly. Use the calculated stake.
Long odds tie up more money
Example: back £10 at 9.00 and lay at 9.60, with 2% commission. The lay stake is £9.39, the liability is £80.79, and you lose 79p either way.
So a £10 bet needed about £81 sitting at the exchange. Before you place the back bet, check you have the full liability in your exchange account. If you don't, the back is on and the lay can't go on. Then you're gambling £10 on an outsider with nothing to cover it.
Reading the exchange screen
An exchange shows two prices for each selection. One is the top price you can back at. The other is the top price you can lay at. The lay price is usually a little higher than the back price, and the gap is narrower in busy markets.
Under each price is the amount of money waiting to be matched. That's called liquidity. Example: say you want to lay £9.84 at 2.56 and only £5 is waiting at that price. About half your lay matches. The rest waits, unmatched, at 2.56 until someone backs at that price, you cancel it, or the exchange cancels it at the start (see mistake 4). Our guide to betting exchanges covers liquidity in more detail.
What goes wrong with lay bets
A Bournemouth University study, reported in September 2026, surveyed 2,112 UK matched bettors. It found over half had lost money overall, and it named three mistakes people made: a miscalculation, a misread offer and the wrong button. Mistakes 1 and 5 below are the lay-bet versions of the miscalculation and the wrong button. The other three come from how exchanges work.
Typing the liability into the stake box. Some people see £15.35 in a calculator and type it as the lay stake. Now you've laid far more than you meant to. Read which box you're filling in.
The lay never goes on. The exchange page stalls after the back and you get distracted. Place the lay straight after the back and wait until it shows as matched.
The price moves. You saw 2.56, but by the time you reach the exchange it's 2.70. Your qualifying loss grows. Work it out again with the price you actually get.
The lay is part matched, and the rest sits unmatched. On Betfair, unmatched bets are cancelled when the event starts, unless you've set them to Keep or to Take SP (turn them into a bet at the starting price). In football, bets without Keep are also cancelled when a goal, penalty or red card suspends the market. Smarkets cancels them when the market halts before going in play, unless you set each bet to "Keep in-play". Check every lay is fully matched before the start.
Laying the wrong thing. That could be the other team, the draw, a different match on a different day, or the win market when you meant the place market. Check the selection, market and start time on both bets.
When not to lay at all
If you can't afford the liability without worrying about it, don't place the bet. If you're already finding it hard to stop gambling, the exchange isn't the place to start.
Work out your first lay
Run a few numbers before you place anything. Put a back price, a lay price and your commission into the 2UP Calculator and watch the lay stake and liability move.
Checked against Betfair's, Smarkets' and Matchbook's terms on 14 November 2026.
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