Costco reported net sales of $29.9 billion for its December retail month (the five weeks ended Jan. 4, 2026), representing an 8.5% year-over-year increase and a modest acceleration from November’s 8.1% growth. More tellingly, total adjusted comparable sales rose 6.2%, driven by U.S. warehouse comp sales of 6.3%—up from 5.8% the prior month—underscoring sustained demand resilience even as inflationary pressures and foreign-exchange fluctuations continue to challenge peers.

Costco’s digitally-enabled comparable sales jumped 18.3% in December, up from 16.3% in November, marking a critical inflection point for a retailer long known for its in-warehouse treasure-hunt experience. This acceleration suggests that members are increasingly using Costco’s online and mobile channels alongside traditional visits, helping offset any headwinds in physical foot traffic and reinforcing the company’s ability to monetize e-commerce without sacrificing its low-price value proposition.

In the first quarter of fiscal 2026 (ended Nov. 23, 2025), Costco delivered net sales of $66 billion, up 8.2% year over year, while operating income grew 12.2%, outpacing top-line expansion. Membership fee income climbed 14% to $1.33 billion, reflecting both higher renewal rates and steady growth in executive-level subscriptions. The combination of fixed-fee membership revenue and tight cost controls behind Costco’s thin gross margins continues to drive significant operating leverage.

Despite robust fundamentals, Costco trades at a trailing price-to-earnings ratio of 49, implying investors are paying $49 for each dollar of reported profit. While a premium valuation is justified by the company’s unique membership model and consistent comp growth, any unexpected deceleration—whether from broader economic weakness, saturation in key markets or intensifying competition from Sam’s Club and Amazon—could trigger a meaningful re-rating, suggesting a limited margin of safety for prospective buyers.