Stocks have rarely been this expensive. That doesn’t (necessarily) mean they’re headed for a crash.

Robert Shiller, a finance professor at Yale University, who won a Nobel Prize in economics in 2013, measures how expensive stocks are by taking the price of the S&P 500 index, dividing by the average of its past 10 years of earnings and adjusting both the price and the earnings for inflation.
The gauge is known as the cyclically adjusted price/earnings ratio, or CAPE

Today, at a CAPE of 37.1 times adjusted earnings, stocks are significantly above their early record of 32.6 in September 1929 and not far from their all-time high of 44.2 in December 1999. 

The respected investor Jeremy Grantham recently wrote that U.S. stocks and other assets are so overpriced that they constitute a “superbubble,” setting up “the largest potential markdown of perceived wealth in U.S. history.”
https://englundmacro.blogspot.com/2022/01/jeremy-grantham-says-goldilocks-era-of.html

“The problem is, we don’t know,” says Prof. Shiller with a dry laugh.

Jason Zweig WSJ 11 Feb.  2022

https://www.wsj.com/articles/the-trouble-with-a-stock-market-bubble-11644595216

How concerned should you be that the CAPE for the U.S. stock market is the highest in the world? 

https://englundmacro.blogspot.com/2021/05/how-concerned-should-you-be-that-cape.html