Ameritrade, the online broker, said on Tuesday that its quarterly profit rose 21 per cent to $75m, as higher interest income and lower expenses offset a decline in revenue from commissions and clearing fees.

Ameritrade agreed last month to buy rival TD Waterhouse from Toronto-Dominion Bank, marking a consolidation of the struggling online brokerage sector. Previously, it rejected two takeover approaches from E*Trade, another rival online brokerage.