1 Stat That Makes Costco Hard to Ignore this September

Costco's digitally enabled comparable sales rose 20.9% in fiscal 2026, versus 8.4% total comparable-sales growth, with digital sales exceeding $27 billion and representing nearly 10% of fiscal 2025 net sales. Q4 digital comparable-sales growth slowed to 19.5%, and August growth was 17.9%, while the segment carries lower gross margins than warehouse operations. With Costco trading at about 40.8x fiscal 2027 consensus EPS of $22.70, its Sept. 24 Q4 earnings report must demonstrate that digital engagement is improving member economics and profitability to support the premium valuation.

Analysis

COST’s key valuation risk is not whether digital demand grows, but whether digital mix dilutes merchandise margin faster than personalization lifts basket size, renewal propensity, and vendor-funded advertising income. At a premium earnings multiple, even modest evidence of gross-margin pressure or a reduction in traffic/basket momentum can drive disproportionate multiple compression; the market needs proof that digital is accretive to member lifetime value rather than merely shifting transactions from warehouses to lower-margin fulfillment channels.

The Sept. 24 report is a near-term binary catalyst. Focus on reported gross margin excluding fuel/FX, membership-fee income growth, renewal rates, paid-member growth, digital fulfillment expense, and any disclosure on advertising or delivery economics. A deceleration in digital growth is less important than whether management indicates incremental digital sales are cannibalistic; conversely, evidence that personalization raises attachment rates without increasing fulfillment subsidies would support a 6-18 month earnings-upgrade path.

Competitive effects are asymmetric: Walmart (WMT) and Amazon (AMZN) have more mature digital fulfillment and advertising ecosystems, so Costco’s digital expansion may require sustained investment before it generates comparable contribution profit. The contrarian read is that consensus may over-penalize the lower gross-margin mix while underestimating higher-margin ancillary monetization—membership retention, retail media, travel, and supplier economics—but that upside remains unverified until segment-level profitability or improved consolidated margins emerge.

Key Decisions for Investors

• Maintain a tactical underweight in COST into Sept. 24; avoid adding at the current premium multiple unless management demonstrates stable-to-expanding merchandise margin and membership economics. Cover the underweight if the company guides to sustained margin expansion or reports material acceleration in fee-income growth.
• For a defined-risk event expression, buy a 1-2 month COST put spread centered roughly 5-10% below spot rather than outright puts. The thesis is multiple compression on any margin/fulfillment-cost disappointment; risk is a strong renewal-rate and margin print causing a valuation squeeze.
• Use a long WMT / short COST pair over the next 1-3 months if COST’s report confirms digital-margin dilution. WMT offers greater embedded digital-ad and fulfillment scale, while the pair isolates relative execution; exit if COST shows clear incremental-margin improvement or WMT’s U.S. comp trend deteriorates materially.
• Set an alert for post-earnings changes in gross margin, membership-fee income, and renewal rates rather than headline digital growth. A positive recommendation requires evidence that these metrics improve concurrently; absent that evidence, digital growth alone is not a sufficient earnings catalyst.