Betfair's Tennis Exchange commission rate typically ranges from 2% to 5% of the net winnings on trades, although the specific rate can vary based on the user's trading activity and promotion status. The commission is calculated based on the net profit made from winning bets after deducting losing bets, which means that if a bettor incurs a loss, they will not pay commission on that amount. Additionally, Betfair may offer lower commission rates as part of promotional incentives or for customers who have achieved a certain level of activity on the platform, which can effectively encourage more trading and engagement.