Back / Lay Calculator
Size a lay bet against a back bet on an exchange, with commission and liability worked out.
Back / Lay Calculator
Size a lay bet on an exchange against a back bet, with commission taken into account.
Charged on net winnings, typically 2–5 %
Lay stake
₦983.61
Liability
₦2,065.57
If back wins
−₦65.57
If lay wins
−₦65.57
Liability is what the exchange holds while the bet is open — you need it in your balance on top of the back stake, not just the lay stake.
How a Betting Exchange Works
An exchange does not set prices. It matches bettors against each other: one person backs a selection, another lays it, and the exchange takes a commission on the winner's net profit. Laying is what a bookmaker normally does — accepting a bet and paying out if it wins.
Because you can be on either side, an exchange lets you close a position deliberately: back at one price, lay at another, and the two together fix your result.
The Formula
- Lay stake: S_lay = (O_back × S_back) ÷ (O_lay − c), with c the commission as a decimal
- Liability: S_lay × (O_lay − 1)
- If the back wins: S_back × (O_back − 1) − liability
- If the lay wins: S_lay × (1 − c) − S_back
When the lay stake is right, those last two come out equal — that is the check that the position is balanced.
Example
You back ₦1,000 at 3.00 with a bookmaker and lay the same selection at 3.10 on an exchange charging 5 % commission.
- Lay stake: (3.00 × ₦1,000) ÷ (3.10 − 0.05) = ₦983.61
- Liability: ₦983.61 × 2.10 = ₦2,065.57
- If the back wins: ₦2,000 − ₦2,065.57 = −₦65.57
- If the lay wins: ₦983.61 × 0.95 − ₦1,000 = −₦65.57
Identical either way — the position is matched. The ₦65.57 is the qualifying loss, and it is the number any free bet or bonus has to beat for the exercise to be worth doing.
Watch the Liability
The lay stake is ₦983.61 but the exchange holds ₦2,065.57 while the market is open. At longer prices the gap widens sharply: laying at 10.00 ties up nine times the stake. Sizing positions by lay stake rather than liability is the most common way to run out of exchange balance mid-strategy.
Frequently Asked Questions
What is liability on a lay bet?
It is what you pay out if the selection you laid wins: lay stake × (lay odds − 1). Laying ₦1,000 at 3.10 carries ₦2,100 of liability, and the exchange holds that amount from your balance until the market settles. It is the number that matters for bankroll, not the lay stake.
How does commission change the lay stake?
The exchange takes a cut of your net winnings, so a winning lay returns slightly less than the stake. The lay stake is therefore divided by (lay odds − commission) rather than lay odds alone, which nudges it down a little. At 5 % commission the difference is small but enough to unbalance a position if ignored.
What is the difference between backing and laying?
Backing is betting that something will happen — the traditional bet. Laying is betting that it will not: you take the other side, acting as the bookmaker. Exchanges let you do both, which is what makes it possible to close a position at a known profit or loss.
Why does the calculator show a loss?
Because lay odds are normally a little longer than back odds, and the exchange takes commission on top. Matching a bet therefore costs a small amount — the qualifying loss. Matched betting works when a free bet or bonus is worth more than that loss, not because the matching itself makes money.
Related Tools
- Hedging Calculator — the same idea at a traditional bookmaker, without commission.
- Arbitrage Calculator — cover a market across bookmakers rather than back-and-lay.
- Cash Out Calculator — compare closing a position on the exchange against the bookmaker’s offer.