Liability calculation
Betfair's exchange guide defines back, lay, liability and matched status for its product. For lay odds d and backer stake s:
Liability = (d - 1) x s
Laying 20 units at 3.50 creates liability of (3.50 - 1) x 20 = 50 units.
- If the selection occurs, the layer loses 50 units.
- If it does not occur, gross market winnings are 20 units before commission.
Matching matters
An unmatched request is not yet fully accepted. A 20-unit request may be partially matched at one price and completed at another, creating an average price and liability different from the headline screen. Matched bets are governed by the exchange's market information and rules; Betfair's general rules are one current example.
Commission example
If gross net market winnings are 20 units and the applicable commission rate is 5%, commission is 20 x 0.05 = 1 unit and the net is 20 - 1 = 19 units. Betfair's commission page states that its applicable rate is account- and market-dependent, so 5% here is illustrative.
Lay one outcome or back the alternatives?
In a three-way match-result market, laying Home covers Draw and Away under the exchange's settlement definition. Backing Draw and Away separately can create a different payoff because the prices, stakes, commission and partial matching differ. Compare outcome-by-outcome net profit rather than assuming the two structures are identical.
| Match outcome | Lay Home | Back Draw + Away |
|---|---|---|
| Home | Liability lost | Both back bets lose |
| Draw | Backer stake won, less commission | Draw return, Away loses |
| Away | Backer stake won, less commission | Away return, Draw loses |
Keep stake, liability and return distinct
For a lay bet, the backer's stake is not the layer's maximum loss. At lay odds of 3.50 with a 20-unit backer's stake, liability is (3.50 - 1) x 20 = 50 units. If the selection loses, the layer's gross market win is 20 units before commission. If it wins, the layer loses the 50-unit liability.
This asymmetry makes a receipt table useful:
| Field | Example |
|---|---|
| Lay odds | 3.50 |
| Backer's stake | 20.00 |
| Layer liability | 50.00 |
| Gross win if selection loses | 20.00 |
| Gross loss if selection wins | 50.00 |
Account for partial matching
An exchange request may be matched at more than one price or only in part. If 8 units match at 3.40 and 12 at 3.60, calculate each liability separately: 8 x 2.40 = 19.20 and 12 x 2.60 = 31.20, for total liability of 50.40 units. Do not multiply the whole stake by whichever price remains visible later.
Before treating a lay as the opposite of a sportsbook bet, check market definition, available size, commission and settlement information. Betfair's exchange guide documents matching for its product; other exchanges can use different rules.
Related resources
Read the concise lay bet definition or compare exchange and bookmaker odds.
Continue learning
- Next guide: Odds Movement
- Related guide: Probability for Betting Odds
- Definition: Lay Bet
Assumptions and limitations
Examples assume full matching, one settlement outcome and no premium or additional charge. Exchange interfaces, commission rates, liquidity and rules vary. Check the receipt and market information before treating displayed liability as final.
GambleAware
GamCare
Gambling Therapy
GAMSTOP