Costco Wholesale Corporation Reported Sales Results for the five weeks and eighteen weeks ended January 6, 2019. The company reported net sales of $15.42 billion for the retail month of December, the five weeks ended January 6, 2019, an increase of 7.8% from $14.30 billion last year. For the eighteen weeks ended January 6, 2019, the Company reported net sales of $52.99 billion, an increase of 9.5% from $48.39 billion during the similar period last year.