A lay to back calculator converts a betting exchange lay price into the equivalent bookmaker back odds, accounting for exchange commission. Use it to compare exchange and bookmaker prices on equal terms, or to find the minimum back odds needed to profit on a matched bet.
Worked Example: Lay 3.00 at 5% Commission
You see a lay price of 3.00 on Betfair (5% commission). What is the equivalent back odds that breaks even?
If a bookmaker offers better than 1.48 on the same outcome, backing at the bookmaker and laying 3.00 on Betfair is a guaranteed profit.
Cross-Exchange Commission Comparison
Commission rate has a direct impact on equivalent back odds. At the same lay price of 3.00:
| Exchange | Commission | Equiv. back odds (lay 3.00) |
|---|---|---|
| BFB247 | 2% | 1.49 |
| Smarkets | 2% | 1.49 |
| Betfair | 5% | 1.48 |
Lower commission means you keep more of the edge. Verify current rates on each exchange's terms page.
When to Use Lay to Back Conversion
- Matched betting qualifying bets: find the minimum back odds needed at the bookmaker for the lay at the exchange to produce a guaranteed small loss (or profit).
- Arbitrage detection: convert the exchange lay into back-odds terms and compare directly with bookmaker prices.
- Trading: assess whether the lay you are offering on the exchange represents good value relative to bookmaker markets.
Worked Example: Step-by-Step Calculation
The calculator above loads with a lay price of 3.00, 5% commission and a $100 stake by default. Here is exactly how those three inputs turn into the equivalent back odds, implied probability and potential profit shown in the result card.
Step 1: Convert commission to a decimal
Step 2: Solve for equivalent back odds
Step 3: Derive implied probability
Step 4: Calculate potential profit on the $100 stake
Every figure above matches the default result card: 1.48 equivalent back odds, 67.8% implied probability and $47.50 potential profit on a $100 stake. Change any input and the calculator re-runs the same four steps instantly.
Common Mistakes When Converting Lay to Back
- Forgetting exchange commission. Treating the raw lay price as the break-even back odds overstates the edge. On the default example, ignoring commission would suggest 3.00 is the break-even point; the real figure is 1.48 at Betfair's 5% commission and 1.49 at a 2% exchange like BFB247 or Smarkets, a $1.50 difference in potential profit on a $100 stake between the two rates.
- Comparing to gross instead of net return. The equivalent back odds already has commission deducted from the winning lay. Comparing a bookmaker's back price against the raw lay price, instead of the commission-adjusted 1.48, makes the exchange price look better than it actually pays out.
- Mixing up lay stake and liability. The amount you lay is not the amount you risk. Laying $100 at odds of 3.00 creates a liability of stake x (odds - 1) = $100 x 2.00 = $200, the amount the exchange holds if the bet loses. Entering liability where the calculator expects stake, or the reverse, produces a profit figure for the wrong bet size.
- Assuming the equivalence holds if the odds move. The 1.48 equivalent back odds is only valid at the exact lay price of 3.00 used to derive it. If the exchange price drifts before the matching bet is placed, the equivalent back odds changes with it since the formula is tied to that specific quoted price, not a fixed relationship.
Frequently Asked Questions
What is the difference between back odds and lay odds?
Back odds are the price offered when you bet on an outcome to happen. Lay odds are the price at which you offer a bet against that outcome on an exchange. Because the layer wins when the event does not occur, lay odds are always greater than 1.00 and describe the opposite side of the same probability.
How does exchange commission affect lay-to-back conversion?
Commission is charged on winning lays, so the equivalent back odds must be lower than the raw lay price. The formula is: back odds = 1 + (1 - commission) / (lay odds - 1). At 5% commission a lay of 3.00 is equivalent to backing at 1.48, not 3.00.
Can I use this calculator for Betfair and Smarkets?
Yes. Enter 5% for Betfair or 2% for Smarkets (and most other low-commission exchanges). The conversion works for any exchange: just enter the commission rate your account is charged.
When should I convert lay odds to back odds?
Use the conversion when comparing a bookmaker back price with an exchange lay price for the same outcome, or when calculating whether a matched betting qualifying bet is value. The converted figure tells you the minimum back odds you need at a bookmaker to break even after exchange commission.
What commission rate should I use for BFB247?
BFB247 charges 2% commission on winning bets. This is lower than Betfair's standard 5%, which means your equivalent back odds are closer to the raw lay price, keeping more profit on matched bets.