Back/Lay Calculator
Calculate optimal lay stakes for matched betting and trading
Formula:Lay Stake = (Back Odds × Stake) / (Lay Odds - Commission)
Bet Type
Lock in equal profit regardless of outcome
Back Bet (Bookmaker)
Your qualifying/cash bet
$
Lay Bet (Exchange)
Exchange odds and commission
%
Matched Bet Results
Qualifying loss calculated
Recommended Lay Stake
$98
Liability: $207
If Back Bet WINS
-$7
Win back bet, pay lay liability
If Back Bet LOSES
-$7
Lose back stake, win lay profit
Calculation Breakdown
Back Bet
$100 @ 3
Lay Bet
$98 @ 3.1
Lay Liability
$207
Commission
$5
Lay Stake
$98
Liability
$207
Avg Profit
-$7
Retention
46.7%
Qualifying Loss: This bet will result in a small loss of approximately $7 to unlock your free bet bonus. This is normal for qualifying bets.
Try These Examples
Common back/lay scenarios
Matched Bet Tracker
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Bet History
0 entries
No bets recorded yet.
Add your first bet to start tracking.
How Back/Lay Matching Works
Understanding matched betting
Example: $100 Qualifying Bet
- 1. Back: $100 @ 3.00 with bookmaker
- 2. Lay: $98.36 @ 3.10 on exchange (5% comm)
- 3. If selection wins: +$200 back win, -$196.72 lay liability = +$3.28
- 4. If selection loses: -$100 back loss, +$93.44 lay win = -$6.56
- 5. Worst case: Small qualifying loss to unlock free bet
Normal Mode
For qualifying bets using real money. Small loss expected.
SNR Free Bet Mode
Stake Not Returned. Different formula for optimal lay stake.
Quick Answer
TL;DR summary
The Back/Lay calculator finds the optimal lay stake to match a back bet. For a $100 back bet at 3.00 odds, laying at 3.10 with 5% commission: Lay Stake = (3.00 × $100) / (3.10 - 0.05) = $98.36. This locks in ~$3.19 profit regardless of outcome. Essential for matched betting and trading positions.
Key Facts About Back/Lay Matching
Important things to know
- Back/lay matching locks in profit regardless of outcome
- Normal mode: Lay Stake = (Back Odds × Stake) / (Lay Odds - Commission)
- SNR Free Bet: Lay Stake = ((Back Odds - 1) × Stake) / (Lay Odds - Commission)
- SR Free Bet: Lay Stake = (Back Odds × Stake) / (Lay Odds - Commission) - same as normal
- Closer back and lay odds = higher profit retention
- Underlay: Accept more profit if back wins, loss if back loses
- Overlay: Accept more profit if back loses, loss if back wins
- Aim for lay odds within 0.1-0.2 of back odds for best results
Frequently Asked Questions
Common questions about back/lay matching
What is back/lay matching?
Back/lay matching involves placing a back bet with a bookmaker and a lay bet on an exchange on the same outcome. By calculating the correct lay stake, you can guarantee the same profit (or loss) regardless of whether the selection wins or loses. This is the foundation of matched betting.
What is a qualifying bet?
A qualifying bet is a bet placed to unlock a free bet bonus. The goal is to minimize losses while meeting the bookmaker's requirements. By back/lay matching a qualifying bet, you typically lose 1-3% of the stake due to odds differences and commission, but gain access to a valuable free bet.
What's the difference between SNR and SR free bets?
SNR (Stake Not Returned) free bets only return winnings, not the stake. SR (Stake Returned) free bets return both winnings and stake. SNR free bets require a different lay stake calculation since you won't get the stake back if you win. SNR is more common.
What is underlay and overlay?
Underlay means betting less on the lay side than optimal, accepting more profit if the back wins but a loss if it loses. Overlay means betting more on the lay, accepting more profit if the back loses but a loss if it wins. Both are used for strategic reasons or when exact matching isn't possible.
Why might back and lay odds be different?
Exchange odds (lay) may differ from bookmaker odds (back) because: exchanges charge commission, markets have spreads between back and lay prices, bookmakers may have better odds on promotions, and market efficiency varies between platforms.
How much profit can I expect from matched betting?
From qualifying bets: expect 0-5% loss. From free bets: expect 70-95% profit of the free bet value depending on odds. A $50 free bet typically returns $35-47 profit. Higher back odds and closer lay odds increase returns.
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).