The important input is net market profit
Imagine one settled bet in a market makes £80 profit and another loses £30. The pre-commission market result is £50. With a hypothetical 5% effective rate, commission is £2.50 and the net result is £47.50. Charging 5% on the £80 alone would incorrectly charge £4 in this net-market model.
Profit is different from the amount returned
A £20 back bet at decimal odds 4.00 has an £80 return when it wins, comprising £20 returned stake and £60 profit. If this is your only bet in the market, enter £60. At a hypothetical 5% rate the commission is £3, leaving £57 profit. A balance credit of £77 would include the returned £20 stake. The calculator’s headline deliberately shows £57, the profit.
commission = max(net market profit, 0) × effective rate ÷ 100after-commission result = net market profit − commissionDo not net unrelated markets together
A £50 profit on one market and a £50 loss on another do not necessarily cancel for commission purposes. At a hypothetical 5% rate on the winning market, the two results would total a £2.50 loss after that charge. Run each settled market separately using its own applicable rate and then combine the after-commission results.
Find your actual rate
Betfair’s help describes commission on positive net winnings in a market. The applicable rate can depend on account arrangements and market conditions. Use the effective rate shown for your account and market; the default input is an illustration, not a statement that every GB customer pays 2%.
Losses, zero and rounding
A zero or negative market result gives zero commission in this model. Positive commission is rounded to the nearest penny, half pennies up. For very small amounts, check the operator’s actual rounding policy. Other charges can exist separately; this tool is not a complete account statement.
Primary sources
Betfair: how commission is calculated and Betfair: charges. Reviewed . Examples here are original hypothetical arithmetic, not a quoted tariff.