The results fell short of Wall Street projections. Analysts, on average, had forecast profit of 31 cents per share, on revenue of $713.6 million, according to data provided by FactSet.

Shares of Ameritrade fell in morning trading as the broader markets dropped. The stock lost 27 cents, to $15.95. Shares have changed hands between $13.43 and $22.90 in the past 52 weeks.

The July-to-September quarter was the worst in the markets since the 2008 economic crisis, as worries about the European debt crisis, the U.S. debt ceiling debate and credit rating downgrade and the general health of the world economy whipsawed stocks.

During the period, TD Ameritrade saw average client trades per day of 415,739, up 31 percent from 317,684 per day last year.

CEO Fred Tomczyk said the quarter brought the top five trading days in the company's history. In particular, the U.S. downgrade resulted in one of its busiest days ever. "We processed nearly 900,000 trades in one day with virtually no interruptions for clients. Quite simply, that would not have been possible three years ago," he said during a conference call to discuss results.

Investments in infrastructure and technology can be credited for the company's ability to handle the increased activity, he said.

He noted during the call that the summer months are typically slow for the market. "It is unusual to have record quarter in the September quarter," he said. "Our organization really did take advantage of the uncertainty in the market, and we did pick up a fair bit of business in August and September."

Trading has remained heavy during October, with average client trades per day at 394,000.

Total trades reached 26.6 million for the quarter, up from 20.3 million. The average commissions and fees per trade slid 4 percent to $11.85.

"It was a solid quarter," said David Trone, head of U.S. banks and brokers research at JMP Securities. He said the shortfall compared with Wall Street expectations came mostly because of higher expenses and lower money-market fees.

Money-market fee revenue fell 66 percent to $1.2 million as balances fell. With interest rates near zero, it's difficult to charge fees on money-market accounts, Trone said. "Fee waivers are piling up."

Operating expenses rose 6 percent during the quarter to $435.2 million. Almost all of the increase came from employee compensation and benefits. Clearing and execution costs also rose, reflecting the higher volume.

TD Ameritrade said customers opened 150,000 new accounts during the quarter, for a total of 5.6 million funded accounts. The company ended its fiscal year with a net gain of 162,000 accounts.

New client assets reached $12.4 billion during the period, which the company said translates to an annualized growth rate of 12 percent. The funds were about 60 percent institutional and 40 percent retail, although the majority of the company's clients remain retail investors, the CEO said.

For the full fiscal year, TD Ameritrade earned $637.8 million, or $1.11 per share, up 8 percent from $592.2 million, or $1 per share, for fiscal 2010.

Tomczyk said the company expects the "difficult business environment" to continue through 2012. The company has a few strategies planned, including introducing checking accounts with debit cards in the coming months. "It's nice to be introducing it while the banks are introducing new fees."

The company forecast profit for its next fiscal year will come in between $1 and $1.35 per share. That range encompasses the $1.20 per share annual profit projected by analysts, whose estimates range from $1.10 to $1.45 per share.