The market's being good to discount broker Ameritrade (NASDAQ:AMTD), which said today that earnings for its fiscal fourth quarter should come in at the middle to upper end of its previous guidance of $0.06-$0.14 a share. It earned $0.04 a share in last year's fourth quarter, excluding charges.

August trading activity at the Omaha-based firm was strong, with average daily volume of 137,000 trades. That's below both July's average daily volume of 161,000 and June's 154,000, but is good considering that August is usually a slow month for the markets. Ameritrade expanded its customer base, too, opening 27,000 new accounts and bringing its total number of accounts up to 3 million, a significant milestone for the company.

So far, September's also shaping up well for the broker, which competes with E*Trade (NYSE:ET) and Motley Fool Stock Advisor recommendation Charles Schwab (NYSE:SCH). Ameritrade said that trading volume this month is trending up about 30% over August.

Since March, when trading stagnation finally started turning around for the discount brokers, all three companies' stocks have dramatically risen, with Ameritrade leading the charge. We haven't heard yet from either Schwab or E*Trade about how August went, or how September looks so far, but we're waiting and watching.

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