Shares of big-box retailer Costco (COST) - Get Report are down after hours Thursday after the company reported fiscal-fourth-quarter top- and bottom-line results that missed Wall Street's expectations.

For the quarter ended Sept. 1, the Issaquah, Wash., company reported earnings of $2.47 a share on a 7% increase in revenue to $47.5 billion. Analysts were expecting the company to report earnings of $2.54 a share on revenue of $47.57 billion. 

Complicating matters was an SG&A-related reserve of 22 cents a share for a "product tax assessment."

In general, SG&A charges are incurred to promote, sell or deliver a company's products or just in the management of the overall company. Costco in a statement did not specify the assessment. 

The company reported an adjusted 5.2% increase in comparable-store sales in the U.S., with international comps outside Canada rising 5%. The company's e-commerce operation reported a 21.9% year-over-year increase. 

Costco shares were down 0.9% Thursday after hours after closing the regular session up 1.4% at $289. Year to date, Costco is up 45%. 

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