Back/Lay Bet Calculator
Calculate lay bet liability, back-to-lay trading profits, and lay-to-back green-up amounts for betting exchanges.
Back/Lay Bet Calculator
Odds Format
Calculator Mode
Lay Odds
Backer's Stake
$
Exchange Commission (%)
⚠ Liability Warning
Your maximum liability is $200.00 — this is the amount you could lose if the selection wins.
Lay Bet Analysis
Liability (if loses)$200.00
Profit (if selection loses)+$95.00
Loss (if selection wins)-$200.00
Implied Probability33.3%
Understanding Lay Bets
When you lay a bet, you're acting as the bookmaker. You profit when the selection loses, but your liability (potential loss) can be much larger than the backer's stake.
Quick Reference: Odds Formats
Decimal
Total return per unit staked, including your stake. 2.50 returns $2.50 on a $1 bet.
Fractional
Profit relative to stake. 3/2 means $3 profit for every $2 staked, plus your stake back.
American
Positive shows profit on a $100 stake; negative shows the stake needed to win $100.
Understanding Exchange Betting
On a betting exchange like Betfair, you can both back (bet for) and lay (bet against) outcomes. Laying a selection means you are acting as the bookmaker — you accept someone else’s bet and pay out if they win.
Key Concepts
- Back Stake: The amount you bet on a selection to win
- Lay Stake: The amount you accept from a backer
- Liability: Your maximum loss when laying = Lay Stake × (Lay Odds − 1)
- Commission: The exchange takes a percentage (usually 2-5%) of net winnings
Lay Bet Example
You lay $10 at odds of 4.00:
- Liability = $10 × (4.00 − 1) = $30
- If the selection loses: You win $10 minus commission
- If the selection wins: You lose $30 (your liability)
Back-to-Lay Trading
Back a selection at higher odds, then lay it at lower odds after the market moves to lock in a guaranteed profit regardless of the outcome. This is called “greening up”.
Trading Example
You back at 5.00 ($10 stake) then lay at 3.00:
- If you lay $16.67 at 3.00, your profit is approximately $6.67 whether the selection wins or loses
- This technique is used by professional exchange traders who profit from odds movements rather than predicting outcomes