Costco: Why September Growth Reads 13.0%, 11.4% and 7.6%

A retail sales percentage becomes useful for COST research when its definition stays attached. Costco's September release gives three growth rates for the same five-week period. Keeping them in separate rows helps you compare the next update without switching measures midway.

Original SignalSage research graphic in ivory, burgundy and charcoal. Three equal cards label Costco September 2026 growth: net sales 13.0%, total-company comparable sales 11.4%, and comparable sales excluding gasoline-price changes and foreign exchange 7.6%. All cover the five weeks ended October 4. A footnote notes a Labor Day timing benefit of a little over 50 basis points. Historical company-reported sales, not profit, a forecast or an app test.

Start with the same reporting window

Costco announced the update on October 7, 2026. Its retail September covered five weeks ended October 4, rather than the calendar month alone. Net sales reached $30.02 billion versus $26.58 billion a year earlier, up 13.0%.

Name the measure before comparing it

Total-company comparable sales increased 11.4%. The comparable-sales figure excluding changes in gasoline prices and foreign exchange was 7.6%. Those two comparable-sales rates differ by 3.8 percentage points; that calculation combines the stated exclusions and does not isolate gasoline's contribution. The 13.0% net-sales growth uses a different measure from either comparable-sales row.

Keep the calendar effect visible

The company also says the later Labor Day positively affected total and comparable September sales by a little more than 50 basis points. Record that note separately. The release does not supply a fully calendar-adjusted comparable-sales number, so subtracting an exact 0.50 percentage point would add precision the company did not give.

Use a definition-matched research log

Create a row for reporting period, geography, measure, exclusions and source date. Compare total-company figures with the same total-company definitions next month. Read regional rates in their own rows. This simple discipline makes later revisions and apparent accelerations easier to investigate.

What the release can answer

The update describes reported sales growth and the measurement choices behind it. An earnings view still needs the relevant financial statements, costs and reporting period. Treat the graphic as a source-reading worksheet. It does not estimate a margin, future demand, a stock-price move or an investment return.

Keep original sources beside your notes

SignalSage by MerlaTech provides US Stock Research / AI Stock Analysis for iPhone and Android. Keep company disclosures alongside your research notes and the questions the next report can answer. English UI; some features require in-app purchases or a subscription.

Costco official September sales release, October 7, 2026

SignalSage for iPhone and Android

Original research graphic; AI-assisted writing. Historical company-reported figures checked October 8, 2026. Research education, not personalized investment advice or an app test.

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