TJX Cos., the Framingham company that operates such retail chains as T.J. Maxx, Marshalls, and HomeGoods, said Thursday said that its August same-store sales rose 8 percent when compared with sales from August of last year.

Same-store sales, which include sales only at stores open at least a year, are regarded as an important measure of a retailer’s performance. TJX sometimes refers to same-store sales as comp sales.

“With such strong comp sales in August, we are now expecting earnings per share in the fiscal 2013 third quarter to be near the high end of our previously estimated range of $.56 to $.59,” TJX chief executive Carol Meyrowitz said in a statement.