Investors are being punitive in part because of uncertainty. Spinning off the Yahoo core business and Yahoo Japan is projected to be even more complicated than the original plan to divest Alibaba. It could take another year or more and may still carry a tax liability, albeit a smaller one because the asset is smaller.

Mark May, an analyst with Citigroup, downgraded his rating on Yahoo in anticipation of the execution risk.

Investors were also disappointed that the core business will still be run by the current management team, led by Marissa Mayer, according to Brett Harriss, an analyst with Gabelli & Company. Before Ms. Mayer took over as chief executive of Yahoo in 2012, the company had earnings before interest, taxes, depreciation and amortization, or Ebitda, of $1.4 billion, a figure projected to be $929 million this year.

It may have declined, but with that much Ebitda, Yahoo’s core business cannot be worthless.

On average, analysts value Yahoo’s core based on five times projected Ebitda – some a little higher, some a little lower. That yields a market capitalization of $4.6 billion if Yahoo were an independent company. Tack on the 35 percent stake in Yahoo Japan, worth about $8.6 billion, and you’ve got a $13.2 billion business that could be spun out.