The first few trading days of November started off well enough for Commonwealth Bank of Australia (ASX: CBA) shares.
Shares in the S&P/ASX 200 Index (ASX: XJO) bank stock closed out October trading for $171.64. On 6 November, shares closed the day changing hands for $178.57, putting the stock up 4% early in the month.
But things took a turn for the worse from there.
When the closing bell sounded on 28 November, shares were trading for $152.51.
That saw CBA shares down a sharp 11.2% over the month, significantly underperforming the 3% one-month loss posted by the ASX 200.
Here's what's been happening.
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CBA shares slump on missed expectations
The biggest down day of the month for stockholders came on 11 November. That followed the release of CBA's September quarter results (Q1 FY 2026), with CBA shares closing the day down 6.6%.
Now Australia's biggest bank still reported some solid results.
Highlights included a 2% year-on-year increase in CBA's unaudited cash net profit after tax (NPAT), which came in at $2.6 billion.
The bank also reported a $17.8 billion increase in household deposits over the three-month period, with home loans increasing by $9.3 billion.
Unfortunately, costs were also up materially.
The ASX 200 bank reported a 4% increase in its operating expenses, excluding restructuring/notable items. Management said rising costs were primarily driven by wage and IT vendor inflation.
On the passive income front, CBA paid out $4.4 billion in fully franked dividends in the September quarter.
But with CBA shares trading at a price to earnings (P/E) ratio of around 25 times, the highest of all the big Aussie banks, market expectations for the bank are high. And the September quarterly results look to have fallen short of those expectations.
"We remain focused on supporting our customers, disciplined execution of our strategy, investing in technology to deliver exceptional customer experiences and delivering strong financial outcomes for our shareholders," CommBank CEO Matt Comyn said on the day.
What about the other big four ASX 200 bank stocks?
So, how did the other three big ASX 200 bank stocks compare with the 11.2% losses posted by CBA shares in November?
Well, National Australia Bank Ltd (ASX: NAB) shares fell 8.1% over the month. NAB shares trade on a P/E ratio of around 18 times.
ANZ Group Holdings Ltd (ASX: ANZ) shares slipped 5.5% in November. ANZ shares trade on a P/E ratio of around 15 times.
Westpac Banking Corp (ASX: WBC) shares were the best performers among the big four ASX 200 bank stocks. Shares closed down 3% in November, mirroring the losses posted by the benchmark index. Westpac shares trade on a P/E ratio of around 18 times.
