Because of a 53-week fiscal year, chains including J.C. Penney, American Eagle and Guess have predicted that some third-quarter sales will shift into the second quarter. But recent weakness in mall traffic, and macroeconomic factors such as the slumping housing market, and rising interest rates and energy costs also could serve to suppress sales, particularly for retailers with less clearly defined brands.

"We anticipate that the Q2 benefit from the fiscal calendar shift will be modest at best," the report said, "even after considering the benefit from more tax-free shopping events in this year's July quarter."

A number of states are offering tax-free holidays in July, which should boost sales. In fact, this year will see 23 days of tax-free shopping, compared with eight days last year. But a number of markets will begin their school years much later vs. the fiscal calendar than last year, due to the 53-week calendar shift. That could nullify any gains, the report said.