Lay Bet Calculator
Calculate liability, profit, and stakes for lay bets on betting exchanges
Formula:Liability = Stake × (Odds - 1)
Calculation Mode
Choose what you want to calculate
Lay Bet Details
Enter your lay bet parameters
The odds you're laying at
$
%
Lay Bet Results
Your lay bet breakdown
If Selection WINS
-$200
You pay the backer's winnings (liability)
If Selection LOSES
+$95
You keep the backer's stake (minus commission)
Calculation Breakdown
Lay Odds3.00
Backer's Stake$100
Liability (Odds - 1) × Stake$200
Gross Profit (if you win)$100
Commission (5%)-$5
Net Profit (if you win)$95
Amount Required
$200
Implied Prob
33.3%
Lose Prob
66.7%
Risk/Reward
2.11:1
Important: You need $200 in your exchange account to cover the liability. This amount will be held until the event settles. If the selection wins, you lose this amount. If it loses, you profit $95.
Try These Examples
Common lay bet scenarios
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How Lay Betting Works
Understanding exchange lay bets
Example: Laying a Horse at 4.00
- 1. Someone backs: $100 on the horse to win at 4.00
- 2. Your liability: $100 × (4.00 - 1) = $300
- 3. If horse WINS: You pay $300 (their winnings)
- 4. If horse LOSES: You keep $100 × (1 - 5%) = $95
Back vs Lay
Back = Betting FOR something to win
Lay = Betting AGAINST something to win
Common Uses
Matched betting, trading, hedging positions, or simply when you think something won't win.
Quick Answer
TL;DR summary
A lay bet is betting AGAINST an outcome - you win if the selection loses. On a betting exchange, laying at 3.00 odds for $100 stake means: Liability = ($100 × (3.00-1)) = $200 you could lose if selection wins. Profit = $100 × (1-5% commission) = $95 you win if selection loses. Always know your liability before placing lay bets!
Key Facts About Lay Betting
Important things to know
- Lay betting means betting against an outcome (it WON'T win)
- You act as the bookmaker - accepting bets from backers
- Liability = Stake × (Odds - 1) - this is your potential loss
- Profit = Stake × (1 - Commission) - paid if selection loses
- Betfair commission is typically 2-5% depending on status
- Lower lay odds = more likely to happen = higher implied probability
- Lay bets are essential for matched betting and trading
- Exchange minimum stake is usually $2
Frequently Asked Questions
Common questions about lay betting
What is a lay bet?
A lay bet is the opposite of a traditional "back" bet. Instead of betting that something will win, you're betting that it won't win. You're essentially acting as the bookmaker, accepting someone else's bet. If the selection loses, you win their stake (minus commission). If it wins, you pay out their winnings.
What is liability in lay betting?
Liability is the amount you stand to lose if the selection wins. It's calculated as: Liability = Stake × (Odds - 1). For example, if someone backs a horse at 4.00 for $50, your liability is $50 × 3 = $150. This amount is held by the exchange until the event settles.
How is commission calculated?
Commission is charged on your net winnings only (when you win). Standard Betfair commission is 5%, but can be as low as 2% for frequent traders. If you lay $100 at 3.00 odds and win, your gross profit is $100, but after 5% commission, you receive $95.
Why would I lay bet instead of back bet?
Lay betting is useful when: (1) You think something won't win but can't identify the winner, (2) You want to trade positions by laying after backing, (3) You're matched betting to extract value from bookmaker offers, (4) You believe the odds are too short (selection is overrated).
What happens if there's a dead heat?
In a dead heat, the odds are adjusted. Your liability is reduced proportionally. For example, in a 2-way dead heat, you'd pay out half the normal amount. The exchange handles this automatically when settling bets.
Can I lose more than my liability?
No. Your maximum loss is always your liability, which is held by the exchange when you place the bet. You cannot lose more than this amount. This is why exchanges require you to have sufficient funds to cover liability before accepting your lay bet.
How this works
Calculations follow the published mathematics of the game — combinatorics for cards, probability theory for dice, and expected-value accounting for wagers. Results are verified against independent references (primarily Wizard of Odds). No calculation here is an opinion or recommendation; it is arithmetic applied to the rules of the game.
What this tool can’t do
When to consult a professional
This tool computes probability and expected value. It is not a betting system and cannot predict the outcome of any individual wager. If gambling is causing problems for you or someone you know, call the National Problem Gambling Helpline at 1-800-GAMBLER.
Sources
- [1]Wizard of Odds — Michael Shackleford, ASAIndustrywizardofodds.comAccessed Apr 21, 2026
Actuary; widely cited casino-game probability reference. Used for house-edge and EV verification.
- [2]National Council on Problem GamblingOfficial sourcencpgambling.orgAccessed Apr 21, 2026
Responsible-gambling guidance and 1-800-GAMBLER helpline.
Joseph OrdunaFounder & Software Engineer
Full-stack software engineer specializing in embedded systems, web architecture, and AI/ML. Founder of Practical Web Tools. Built the gesture-controlled drone IP acquired by KD Interactive (Aura Drone, sold on Amazon).