Commonwealth Bank of Australia (ASX: CBA) shares are edging lower today.

Shares in the S&P/ASX 200 Index (ASX: XJO) bank stock closed on Friday trading for $173.84. In morning trade on Monday, shares are swapping hands for $173.51 each, down 0.2%.

For some context, the ASX 200 is just about flat at this same time.

Despite today's dip, however, CBA shares have delivered some benchmark smashing returns over the past 12-months.

One year ago, you could have bought shares in Australia's biggest bank for $120.31 apiece. Meaning the ASX 200 bank stock is up 44.2% at current levels.

And if we add in the $4.75 in fully franked dividends CBA paid to eligible stockholders over this period, then the accumulated value of the big four bank stock has gained an impressive 48.2% in a year.

You're unlikely to hear any shareholders complaining about those kinds of gains.

Of course, that's all come and gone now.

Looking ahead towards 2026, should I still buy CBA shares today?

Well, according to two leading investment experts, most likely not (courtesy of The Bull).

Why CBA shares could be headed for a tumble

"The CBA is a quality company," said Sanlam Private Wealth's Remo Greco, who has a sell recommendation on CBA shares. "The rapid rise in the share price is difficult to justify."

Greco noted, "The share price has risen from $144.41 on April 7 to trade at $172.50 on May 22. In our view, the shares are trading at a significant premium when compared to its major competitors."

Greco added:

The CBA appeals for its established track record of generating strong profits and paying attractive dividends. However, at these levels, we believe the stock is more than priced to perfection and leaves little or no room for disappointment.

Last week's 0.25% interest rate cut from the RBA should offer some tailwinds for the big four bank. But likely not enough to negate a pending increase in non-performing loans.

"A recent interest rate cut will ease the burden, but there's plenty of borrowers still struggling in this cost-of-living crisis," Greco said. "Investors may want to take out some insurance by selling a portion of their shares."

Also selling the big 4 ASX 200 bank stock

Securities Vault's Nathan Lodge also has a sell recommendation on CBA shares (courtesy of The Bull).

With CBA stock trading near record highs, Lodge points to the historically elevated price-to-earnings (P/E) ratio as cause for concern.

According to Lodge:

The share price recently continued its upwards trend to post all-time highs. The price rally recently propelled its price/earnings ratio above 30 times, significantly surpassing its 10-year average of 17 times and positioning it as one of world's most expensive banks.

And Lodge also foresees a potential increase in stressed borrows on the horizon.

He noted:

While CBA reported a robust unaudited cash profit of $2.6 billion in the third quarter of fiscal year 2025, increasing arrears in home loans, personal loans and credit cards signal potential stress among borrowers.

At the recent price levels of CBA shares, he concluded, "Investors may want to consider taking some money off the table."