Jan 3 (Reuters) - U.S. retailer Costco Wholesale Corp has posted a better-than-expected 9 percent rise in December sales at stores open at least a year, mainly helped by an additional sales day in the reporting period.
"This year's December retail month had one additional day compared to last year ... As a result, December total and comparable sales results benefited by approximately 2 percent," said David Sherwood, director of finance and investor relations.
Costco's January sales period will include 34 selling days, as opposed to 35 days last year, he also said on Thursday.
Analysts had expected a 6.5 percent rise in December same-store sales, including the impact of fuel prices and foreign exchange, according to Thomson Reuters data.
Higher fuel prices and a weaker dollar also had a positive impact on comparable store sales, Costco said.
Excluding the effects of fuel and foreign exchange, Costco posted a December same-store sales increase of 8 percent.
The company said net sales rose 12 percent to $11.2 billion in the five weeks to Dec. 30.