Betfair liquidity and partially matched bets
Betfair is a marketplace where you trade bets with other users. Your lay bet will only be matched if another user is prepared to back the same outcome at those odds. The liquidity figure shown below the odds tells you how much money is available at that price. For lay bets, that figure represents the maximum lay stake you can place, not the liability.
What is a partially matched bet?
If your lay stake is larger than the available liquidity, your bet will be partially matched. The available amount is matched immediately, and the remainder sits in the market as an unmatched bet waiting for backers to fill it.
In a high-liquidity market like an EPL match or a top-tier horse race, the unmatched portion may fill within seconds. In lower-liquidity markets it could take much longer, or never fill at all. If the odds move against you while you are waiting, the unmatched bet may not fill at the original price, and you will be left with an unbalanced position.
Only place lay bets when the available liquidity exceeds your required lay stake. Placing into insufficient liquidity is one of the most common causes of unexpected losses in matched betting.
What to do if your bet is partially matched
Do not simply wait and hope the rest fills. The correct approach is to adjust your lay stake using the advanced calculator.
The advanced calculator includes a "Bets Already Matched" section. Enter the details of your partially matched bet there, then enter the new current lay odds in the Lay section. The calculator will work out the additional stake needed to balance your position at the new odds.
After placing the additional lay bet, cancel your original unmatched bet. If you forget to cancel it, the original unmatched amount will also fill eventually and you will end up having laid too much.
When an event starts before you can act
If an event goes in-play before your lay bet is fully matched, Betfair gives you a choice about what to do with the unmatched portion.
Cancel: the unmatched bet is removed. You are left with an unbalanced position on that outcome.
Keep: the unmatched bet stays in the market. It may get filled depending on how the odds move in-play. Note that online in-play sports betting is prohibited in Australia for users with an Australian IP address. In-play horse racing bets are permitted online.
Take SP (horse racing only): Betfair matches your bet at whatever price is available at the start of the race. Your liability stays the same but your stake decreases, which means your qualifying loss will be slightly higher than expected. Selecting Take SP for all racing bets is the recommended default. It guarantees you will not be left completely unmatched going into the race.
How to avoid partial matching
Check the liquidity figure before placing any lay bet. If the available liquidity at the best price is lower than your required stake, check the queue. The numbers alongside the pink box show the next available prices and how much is available at each. For a large bet you may need to factor in that your lay will be filled at multiple odds points.
Bet timing also matters. Liquidity builds as an event approaches. Early markets on lower-profile events can have very thin liquidity, which means odds can move several ticks in a second when a large bet comes in. Waiting until the day of the match, when markets are more stable, reduces both liquidity risk and odds movement risk.