Is Costco Stock Increasing Your Market Risk?
Costco Wholesale (COST) is a $436 billion retailer. Anyone buying the stock likely already holds a portfolio built around the S&P 500. A share that sinks alongside the broader market only multiplies a bad day, while one charting its own course can cushion the blow. So when the market has a bad day, what does Costco do to your money?
Costco Edged Up On The Index’s Average Down Day
Recently, Costco shares have managed to yield a slight gain on the market’s average down day. Over the year to October 14, 2026, the S&P 500 lost 0.585% on its average down day. On those exact days, a $10,000 holding in Costco added about $3.68 in value.
Performance was actually more muted on the market’s good days. On the average up day, the index gained 0.641%, and Costco added just $1.84 to that same holding. The stock barely tracked the wider market at all. Its beta, measuring how far a stock moves for each 1% move in the index, sat at -0.14 over the past year.
Costco is not a calm stock, though. Over the past year, its volatility, measuring how widely a price swings over twelve months, was 19.9%. That compares to 12.7% for the S&P 500. The retailer has not piled onto existing market risk, yet it still subjects investors to wider swings of its own.
If you have held Costco Wholesale for years, your biggest question may be taxes, not its day-to-day swings. See how a tax-aware transition works.
Could Costco Start Tracking The Index Again?
The underlying business remains steady, alongside a recent pickup in growth. Revenue grew 10.1% in the twelve months to August 2026, up from 8.2% growth a year earlier. Furthermore, Costco’s twelve-month operating margin reached 3.9%. That is its highest at any fiscal quarter end in data going back to fiscal Q1 2017. Net sales for the retail month of September rose 13.0% from a year earlier.
The stock’s relationship to the broader market remains far less settled. Over the past year, Costco’s daily moves showed almost no link to the index at all, recording a correlation of -0.09, where zero indicates no connection. However, over the five years to October 14, 2026, that same measure stood at 0.51. That closer tie shows Costco’s shares certainly have moved in line with the market before.
Did Costco’s Bigger Moves Pay Off For Holders?
Costco holders earned more than index holders, though they captured about as much for each unit of swing. Over the five years from October 15, 2021, to October 14, 2026, Costco returned 18.0% a year with dividends included. By comparison, the S&P 500 returned 13.1% a year.
Securing that extra return required stomach for wider swings. Costco’s annual volatility over the same five years was 23.0%, compared to 17.0% for the index. When you divide the return by the volatility, Costco holders earned about 0.78 points of return for each point of swing, edging out the 0.77 points seen in the S&P 500.
Looking at the past year’s pattern, Costco added about $3.68 per $10,000 on the market’s average down day, and about $1.84 on its average up day.
Changing Advisors Does Not Have To Mean A Tax Bill
Long-held positions like Costco Wholesale often carry large unrealized gains, which is exactly why many investors stay with an advisor they no longer love. Accounts usually move in kind, without selling, and concentrated low-basis stock can be unwound gradually with exchange funds, charitable trusts, direct indexing, and staged sales. Our partner firm Empirical Asset Management will show you how a transition would work for your account.