Our monthly market valuation updates have long had the same conclusion: US stock indexes are significantly overvalued, which suggests cautious expectations for investment returns. This analysis focuses on the P/E10 ratio, a key indicator of market valuation, and its correlation with inflation and the 10-year Treasury yield.
The relationship between market valuation, as represented by the P/E10 ratio, and inflation reveals crucial patterns. The following scatter graph illustrates this relationship across three distinct periods: January 1881 to December 2007, January 2008 to February 2020, and March 2020 to the present.
Key observations from the graph include:
The inflation figure presented is the year-over-year change. Note: Due to the lapse in official Consumer Price Index (CPI) reports from the government shutdown, the inflation figure for October 2025 been extrapolated using the two prior months’ data. Additionally, the most recent figure has also been extrapolated since the official CPI report had not been released at the time of writing.
The “sweet spot” of 1.4% to 3.0% inflation has historically supported higher market valuations. Currently, the P/E10 stands at 39.8, with a year-over-year inflation rate of 2.22%. This places us inside the “sweet spot” and within the “extreme valuation territory” previously observed during the tech bubble. This means that the current valuation is very high compared to historical norms, and traditionally, these periods are associated with higher risk of market downturns.
A common question is whether a valuation metric such as the P/E10 has any merit in a world with Treasury yields at low levels. To address this, we examine the correlation between P/E10 and the 10-year Treasury yield.
This chart begins in 1960, as recommended by Ed Easterling of Crestmont Research, because prior to this period, bond yields did not consistently respond to inflation changes.
Key observations include:
The post-financial crisis period presented “uncharted” territory, with P/E10 ratios above 20 and yields below 2.5%. This deviated significantly from historical patterns. The current yield of 4.14% suggests a shift away from this unprecedented period and towards a time similar to that of the tech bubble.
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