Concepts

Back/Lay surebets

A Back/Lay surebet pairs a normal bet at a bookmaker (the back: it WILL happen) with the opposite position at a betting exchange like Betfair (the lay: it will NOT happen). When the bookmaker's price beats the exchange's lay price by more than the commission, the profit is locked whichever way the match goes.

6 min read Updated 2026-07-02

Back/Lay is the gentlest form of arbitrage on your bookmaker accounts and the easiest to misunderstand on the exchange side, because a lay stake is not what the number suggests. Five minutes here saves real confusion later.

What a lay bet actually risks #

Laying means playing the bookmaker's role: you offer the bet and pay out if the outcome happens. When you lay EUR 113.2 at odds 1.39, you are not risking 113.2: you stand to WIN 113.2 (someone's back stake), and you risk the payout above it, called the liability: 113.2 x 1.39 - 113.2 = EUR 44.15.

The exchange locks the liability from your balance while the bet is open. Read every lay twice: the stake is what you can win, the liability is what you can lose.

Commission is part of the odds #

Exchanges charge commission on net winnings (Betfair's base rate differs per market and account; the example uses 6.5 percent). The commission is why a lay at 1.39 is NOT automatically profitable against a back at 1.50: the calculator must shave it off the exchange side before declaring an arb.

In OddStorm you set your own default commission per exchange and the Back/Lay calculator prices every opportunity with YOUR rate, not a generic one. Enter the rate your account actually pays; a wrong commission silently turns thin arbs into losses.

Why arbers love Back/Lay #

Three properties make Back/Lay the account-friendly arm of arbitrage:

Exchanges never limit winners: the lay side of every arb sits somewhere that does not care how sharp you are, so only one side of your activity is visible to a bookmaker.
One counterparty for many arbs: instead of ten soft books on the second leg, the exchange covers them all, simplifying money logistics.
Clean exits: placed one leg and the price moved? The exchange usually still offers SOME lay price, so you can close the position for a small, known cost instead of holding a naked bet.

Back/Lay in OddStorm #

Back/Lay surebets are a separate feed in the OddStorm Desktop App (PreMatch and InPlay), with the exchange commission and liquidity built into the calculation and the lay stake and liability precomputed. The desktop app is Windows-only; that is where Back/Lay lives.

Where to go next #

Back/Lay pairs naturally with account longevity: the limitation-avoidance guide covers the soft-bookmaker side of the same strategy.