Exchange commission

Commission is charged on net winnings in a market, so a losing position pays none and a winning one gives up a percentage of its profit. On a qualifying bet it bites only when the lay wins, which is the outcome where the selection loses. Rates differ between exchanges and can differ between accounts on one exchange, so the figure that counts is the one on the customer's own account.

In matched betting it enters the lay stake as lay odds − commission. Back 10 units at 3.0 and lay at 3.1. With no commission the lay stake is 10 × 3.0 ÷ 3.1 = 9.68 units and the qualifying loss 0.32. At 2% commission (use your own rate) it becomes 10 × 3.0 ÷ 3.08 = 9.74 units and the loss rises to 0.45.

The subtraction has a reason. Without commission, the lay stake that balances both outcomes is back stake × back odds ÷ lay odds. The cut taken from lay winnings means the lay has to be slightly bigger to make up for it, and a smaller divisor does exactly that.

Free bets feel it more, because the amount kept equals the lay's winnings after commission. A 10-unit stake-not-returned free bet backed at 6.0 and laid at 6.2 keeps 8.06 units with no commission and 7.93 at 2%. On each-way and extra-place the rate applies to both lays, win and place.

In the OddsRelay feed

The feed applies no commission and carries no commission field. Lay prices arrive as each exchange quotes them, in lay[].price on the matched feeds and lay_price on raw, and the customer's own rate goes into the tool's arithmetic.

Because rates differ, the lowest lay price is not always the cheapest lay. With the same back bet, laying at 3.15 with 1% commission costs 0.54 units, while laying at 3.1 with 4% costs 0.59, both rates illustrative. A tool that stores a rate per exchange, keyed on lay[].exchange, can compare every lay offer at its true cost.

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