Exhibit 99.1

COSTCO WHOLESALE CORPORATION REPORTS SECOND QUARTER AND YEAR-TO-DATE

OPERATING RESULTS FOR FISCAL YEAR 2017, FEBRUARY SALES RESULTS, AND PLANS FOR MEMBERSHIP FEE INCREASE

ISSAQUAH, Wash., March 2, 2017 – Costco Wholesale Corporation (“Costco” or the “Company”) (Nasdaq: COST) today announced its operating results for the second quarter (twelve weeks) and first half (24 weeks) of fiscal 2017, ended February 12, 2017.

Net sales for the quarter increased six percent, to $29.13 billion from $27.57 billion last year. Net sales for the first half increased four percent, to $56.60 billion from $54.19 billion last year.

Comparable sales for the twelve-week and twenty-four-week periods were as follows:

Comparable sales for these periods excluding the impacts from changes in gasoline prices and foreign exchange were as follows:

Net income for the quarter was $515 million, or $1.17 per diluted share, compared to $546 million, or $1.24 per diluted share, last year. Net income for the first half was $1.060 billion, or $2.41 per diluted share, compared to $1.026 billion, or $2.32 per diluted share, last year.

For the four-week reporting month of February, ended February 26, 2017, the Company reported net sales of $8.92 billion, an increase of eight percent from $8.28 billion during the similar four-week period last year. For the twenty-six week period ended February 26, 2017, net sales were $61.18 billion, an increase of five percent from $58.25 billion during the similar period last year.

Comparable sales for the four-week and twenty-six-week periods ended February 26, 2017 were as follows:

Comparable sales for these periods excluding the impacts from changes in gasoline prices and foreign exchange were as follows:

The Company also announced that, effective June 1, 2017, it will increase annual membership fees by $5 for U.S. and Canada Goldstar (individual), Business, and Business add-on members (“Primary” Members). With this increase, all U.S. and Canada Goldstar, Business and Business add-on members will pay an annual fee of $60. Also effective June 1, annual fees for Executive Memberships in the U.S. and Canada will increase from $110 to $120 (Primary membership of $60, plus the Executive upgrade of $60), and the maximum annual 2% reward associated with the Executive Membership will increase from $750 to $1,000. The fee increases will impact around 35 million members, roughly half of them Executive Members.

Costco currently operates 728 warehouses, including 508 in the United States and Puerto Rico, 94 in Canada, 37 in Mexico, 28 in the United Kingdom, 25 in Japan, 13 in Korea, 13 in Taiwan, eight in Australia and two in Spain. Costco also operates electronic commerce web sites in the U.S., Canada, the United Kingdom, Mexico, Korea and Taiwan.

A conference call to discuss these fiscal 2017 second quarter operating results and February sales results is scheduled for 2:00 p.m. (PT) on March 2, 2017, and is available via a webcast on www.costco.com (click on Investor Relations and “Play Webcast”).

Certain statements contained in this document constitute forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. For these purposes, forward-looking statements are statements that address activities, events, conditions or developments that the Company expects or anticipates may occur in the future. Such forward-looking statements involve risks and uncertainties that may cause actual events, results or performance to differ materially from those indicated by such statements. These risks and uncertainties include, but are not limited to, domestic and international economic conditions, including exchange rates, the effects of competition and regulation, uncertainties in the financial markets, consumer and small business spending patterns and debt levels, breaches of security or privacy of member or business information, conditions affecting the acquisition, development, ownership or use of real estate, capital spending, actions of vendors, rising costs associated with employees (including health care costs), energy and certain commodities, geopolitical conditions, and other risks identified from time to time in the Company’s public statements and reports filed with the Securities and Exchange Commission. Forward-looking statements speak only as of the date they are made, and we do not undertake to update these statements, except as required by law.

CONTACTS: Costco Wholesale Corporation

Richard Galanti, 425/313-8203, Bob Nelson, 425/313-8255, David Sherwood, 425/313-8239

COSTCO WHOLESALE CORPORATION

CONDENSED CONSOLIDATED STATEMENTS OF INCOME

(dollars in millions, except per share data)

(unaudited)

COSTCO WHOLESALE CORPORATION

CONDENSED CONSOLIDATED BALANCE SHEETS

(amounts in millions, except par value and share data)

(unaudited)

Subject to Reclassifications