Betting Exchange Commission: How to Subtract It from Back and Lay Winnings

Exchange commission comes off your net profit on a market, not off each bet. If you have several positions on one market, add them up first: a positive total pays the commission rate, and a negative total pays nothing. For example, a $40 win with 5% commission costs you $2. The 5% is only an example rate, so use the one shown in your account.

Under these assumptions, the $9.50 result requires fully matched bets in one market on one exchange. Moving the back bet to a bookmaker changes the result from $9.50 to $8.10, a reduction of $1.40. Changing the commission rate from 5% to 2% instead changes the same-exchange result from $9.50 to $9.80.

How do you subtract commission from a back bet and a lay bet?

Calculate the market result before commission, then subtract commission from any positive result. If the market result is negative, commission is zero.

For a single winning back bet, profit before commission is back stake × (back odds − 1). This excludes the return of your own stake.

Table A: one back bet, 40 at 5.0

A loss is −$40.00 at any rate, with no commission.

Effective odds after commission express the winning back bet’s payout after the deduction:

Effective odds after commission = 1 + (back odds − 1) × (1 − commission rate)

Use the commission rate as a decimal. Break-even probability is 1 / effective odds after commission. At 5% commission, odds of 5.0 become 4.80, with a break-even probability of 20.83%. This calculation applies to a single position; with several positions, calculate the combined market result first.

For a winning lay bet, profit before commission equals the backer’s stake. Lay liability is what you lose if the selection wins: lay stake × (lay odds − 1). For the underlying mechanics, see how a betting exchange works: back, lay and liability.

Table B: one lay bet, backer's stake 40 at 4.0 (liability $120.00)

Here, break-even probability refers to the selection not winning:

Break-even probability = lay liability / (lay liability + net lay win)

Commission reduces the win but not the lay liability, so the required probability rises.

How do you calculate back and lay bets on one exchange?

Add the back and lay results within the same market before applying commission. In Table C, either outcome produces $10.00 before commission and $9.50 after it.

Table C: back 40 at 5.0 and lay 50 at 4.0 in one market on one exchange, 5% commission

Teaching diagram: a back of 40 at 5.0 and a lay of 50 at 4.0 in one exchange market give 10.00 before commission in both outcomes, 5% commission is 0.50, net profit 9.50Teaching diagram from the article's calculation, not an exchange interface. The 5% commission is the example's assumption.

The lay stake 50 = 40 × 5.0 / 4.0 does not depend on commission: both outcomes give the same profit before commission. This is a green-up, meaning equal profit across the outcomes.

The “commission on every leg” mistake gives +$2.00 when the selection wins and +$7.50 when it does not. Those figures are wrong for one market. Separate commission calculations belong to a different setup when bets are spread across venues; see arbitrage calculator: per-leg commission is correct between venues.

Betfair’s help page “Betfair Charges”, section 4, states that commission applies to net winnings on a market, with none on a net market loss (viewed 23 October 2026, support.betfair.com). Combining positions in Tables C and E is our calculation under that rule, not a quotation from Betfair.

How do you check a bookmaker back bet plus exchange lay in the calculator?

For a bookmaker back bet plus exchange lay, apply commission to the exchange side only. The bookmaker loss does not reduce the exchange market’s commission base, so this example needs a lay stake of $50.63 rather than $50.

The formula is lay stake = back stake × O / (L − c), where O is back odds, L is lay odds and c is commission as a decimal. See hedge bet formulas with an exchange lay for the derivation.

Table D: bookmaker back 40 at 5.0 and exchange lay at 4.0, 5% commission (formula and tool check)

ToolsGambling calculator, Exchange lay mode: back stake 40, back odds 5, lay odds 4, commission 5%, lay stake 50.63, liability 151.90, guaranteed profit 8.10Local ToolsGambling interface, Exchange lay mode: bookmaker back, exchange lay. Values entered for the example; no bets were placed.

Check the example in the hedge calculator, Exchange lay mode:

1. Select the “Exchange lay” tab.
2. Enter 40 in “Back stake”.
3. Enter 5.0 in “Back odds”.
4. Enter 4.0 in “Lay odds (exchange)”.
5. Enter 5 in “Exchange commission (%)”.

The results should show “Lay stake” of $50.63, “Lay liability” of $151.90, and +$8.10 for both “If the back bet wins” and “If the lay wins”. The “Guaranteed profit” label describes the calculated result under the entered assumptions, not a promise about real bets.

Rounding: Table D follows the tool’s unrounded internal calculation. An actual $50.63 lay has lay liability of $151.89 and profits of $8.11 / $8.10, matched within a cent; the tool shows $8.10.

Place the $50.63 lay in the same exchange market as the back bet and the outcomes split: +$7.70 if the selection wins, +$10.10 if it does not. Equal profit there needs $50, not $50.63. This calculator mode does not calculate net market profit for two positions on one exchange.

For free bets or deliberate underlay/overlay calculations, use the appropriate mode in the lay bet calculator.

How do you account for several positions and several markets?

Combine all positions within one market, but calculate separate markets independently. A loss in another market does not reduce commission on a profitable one.

Table E: three positions in one winner market (back A 20 at 3.0, back B 10 at 4.0, lay C 15 at 2.0), 5% commission

Only positive market results attract commission. The final column shows the errors caused by charging each winning position separately.

Example F: two separate markets do not net against each other

Market 1: a 20 at 2.0 back wins, +$20.00, commission $1.00, net +$19.00. Market 2: a 20 at 2.0 back loses, −$20.00, no commission. Total before commission $0.00, after commission −$1.00.

Which commission rate should you enter, and what does it change?

Enter your account’s rate for the relevant market rather than automatically using 5%. Betfair’s “Betfair Charges”, section 4, says rates in My Betfair Rewards regions depend on the chosen package; its Basic package example uses 2% (viewed 23 October 2026, support.betfair.com).

Those regions are the UK, Ireland, Finland, Hungary, Latvia, Croatia and Ukraine. For customers outside the My Betfair Rewards regions, the page edition for other regions gives a discount in certain countries only (section 4.3), and Albania, Australia and New Zealand have no discount (section 4.7). The calculation is:

Commission = net winnings × Market Base Rate × (1 − Discount Rate)

A 5% Market Base Rate with a 40% Discount Rate gives the 3% effective commission assumption below. For Australasian events (Australasian Event) and Master/Sub-Account structures, Betfair charges commission on net winnings (section 4.5), and the package rules and their 2% rate do not apply (section 4.4). The Basic package’s 2% example is not universal. This guide makes no claim about other exchanges’ rules.

Table G: sensitivity of the headline number (Table C green-up; Table D pair)

The bookmaker-back column recalculates the lay stake for each commission rate using the formula in Table D. It does not hold the lay stake at $50.63 while changing the rate.

What changes if your lay bet is only partially matched?

A partially matched lay bet does not produce the calculated equal profit: use only the matched amount, not the full requested stake.

If the back bet of 40 is fully matched and only $30 of the $50 lay in Table C is matched:

• Selection wins: +$70.00 before commission, $3.50 commission, net +$66.50.
• Selection does not win: −$10.00, no commission.

The risk remains open. Submitting an order is not the same as having it fully matched, and neither is the same as settlement after the event.

These calculations exclude markets with several winners, voided bets, dead heats, minimum stakes, odds ticks, exchange rounding, free bets where the stake is not returned and taxes. They also exclude other Betfair charges, including transaction charges at very high bet counts and Expert Fees for a small share of customers, described in “Betfair Charges”, section 3 (viewed 23 October 2026, support.betfair.com).

What should you check before betting?

Check the venue, market, commission rate, matched amounts and outcome calculations before relying on the result.

• Back bet venue: is it on the same exchange or at a bookmaker? These setups need different formulas.
• Market identity: do the positions belong to the same market, rather than merely the same event?
• Commission rate: does the entered rate match your account and the relevant market?
• Matched positions: do the actual matched stakes and odds match your calculation?
• Every outcome: have you checked lay liability, rounding and any charges outside this model?