Interactive Brokers(IBKR 1.71%) had good reason to celebrate this past Memorial Day. The company's key metrics for May were generally higher on both a month-over-month and an annual basis. According to the company's data, its daily average revenue trades, or DARTs -- considered by many to be the most critical figure in the discount brokerage industry -- were roughly 509,000. That's 13% higher when compared with May 2012, and 6% above the preceding month's level.

Also seeing a rise was end-of-month customer equity, which came in at $37.9 billion, 37% higher than at the same time in 2012, and 4% above April's figure.

Ending customer credit balances grew 27% on a year-over-year basis to $22.7 billion, although that number is essentially flat compared with the prior month.