Savvy Nickel
by Robert Shiller
Nobel Prize winner Robert Shiller's landmark warning about stock market and real estate bubbles. First published just before the dot-com crash, updated before the housing crisis, and again before COVID-era market froth. Each time presciently.
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Robert Shiller published the first edition of Irrational Exuberance in March 2000, the exact month the dot-com bubble peaked. The second edition came out in 2005, warning about the housing bubble. The third edition (2015) addressed bond and emerging market froth. His timing has been extraordinary across all three editions.
As of July 2026, the Shiller CAPE ratio stands at approximately 41, the highest reading outside of the 1999-2000 dot-com peak (when it reached 44). The S&P 500 has been driven by AI-related spending and mega-cap technology concentration. Shiller himself noted in a 2025 interview with Barclays that the current market exhibits "narrative-driven" characteristics similar to past bubble periods, though he stopped short of calling it a bubble outright. Whether or not the current market is in bubble territory, Shiller's framework for understanding how bubbles form, how to identify them, and what investors can do about them remains essential reading.
| Attribute | Details |
|---|---|
| Title | Irrational Exuberance |
| Author | Robert J. Shiller |
| Publisher | Princeton University Press |
| First Published | 2000 |
| Third Edition | 2015 |
| Pages | 358 |
| Reading Level | Intermediate |
| Amazon Rating | 4.4/5 stars |
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Robert Shiller is Sterling Professor of Economics at Yale University and a 2013 Nobel Prize laureate in Economics (shared with Eugene Fama and Lars Peter Hansen). Fama's efficient market hypothesis directly contradicts Shiller's bubble theory, making the shared prize one of the more ironic in the award's history. Shiller co-created the Case-Shiller Home Price Index and developed the CAPE ratio (also called the Shiller P/E). He is among the few academic economists who have successfully warned about specific asset bubbles before they burst. His later book, Narrative Economics (2019), expanded on the idea that economic events are driven by popular stories, a concept that has gained renewed attention with the rise of AI-driven market narratives in 2025 and 2026.
The Cyclically Adjusted Price-to-Earnings ratio is Shiller's most practically important contribution to investing.
CAPE Ratio = Current Stock Price / Average Inflation-Adjusted Earnings (10-year average)Unlike the standard P/E ratio (which uses last year's or next year's earnings), CAPE uses 10-year average earnings, smoothing out the cyclical fluctuations that make single-year P/E misleading.
Why 10-year averaging matters:
| Year | Single-Year P/E | CAPE (10-year) |
|---|---|---|
| 2009 (crisis trough) | 122 (earnings collapsed) | 13 (earnings averaged over 10 years) |
| 2000 (dot-com peak) | 32 | 44 (all-time record at time) |
| 1982 (secular bear market trough) | 8 | 7 (historically cheap) |
| 2024 | ~25 | ~36 (historically elevated) |
| 2026 (July) | ~28 | ~41 (near dot-com peak levels) |
At the 2009 trough, the single-year P/E suggested the market was wildly expensive (earnings had collapsed), while CAPE correctly identified it as cheap by historical standards. The reverse happened at the 2000 peak. The July 2026 CAPE reading of approximately 41 puts current valuations near the dot-com peak of 44, driven largely by AI-related spending and mega-cap technology concentration in the S&P 500.
Shiller presents one of the most important charts in investing: the relationship between CAPE at time of investment and subsequent 10-year returns.
| CAPE at Investment | Subsequent 10-Year Average Annual Return |
|---|---|
| Below 10 | +18% per year |
| 10-15 | +15% per year |
| 15-20 | +11% per year |
| 20-25 | +7% per year |
| 25-30 | +4% per year |
| Above 30 | +1% per year (near zero or negative in some cases) |
The implication: Starting valuation matters enormously for long-term returns. Buying at CAPE of 10 has historically produced 18% annual returns. Buying at CAPE of 35+ has historically produced near-zero 10-year returns. This is not timing the market. It is understanding the mathematical relationship between price and long-run return. For a practical tool, see our investment return calculator.
Shiller is honest about his ratio's limitations:
A 2024 study by Research Affiliates' Rob Arnott and colleagues, published in the Journal of Portfolio Management, found that adjusting CAPE for changes in payout ratios (buybacks versus dividends) and intangible capital improves its predictive power. Their "Adjusted CAPE" still showed the U.S. market as significantly overvalued in 2024, but less so than the raw CAPE suggested. The debate continues, but the core insight holds: starting valuation is the single best predictor of long-run returns.
Despite these limitations, CAPE remains one of the most reliable long-run valuation indicators available to individual investors.
Shiller identifies the structural factors that amplify market bubbles:
Technological change: New technology creates genuine uncertainty about future earnings that rational valuation models cannot capture. This uncertainty provides cover for speculative excess. The internet was genuinely revolutionary, but the speculation about valuations in 1999 was not rational. The same pattern is visible in 2025-2026 with AI-related stocks. NVIDIA, for example, traded at a forward P/E above 50 at points during 2024-2025, and the "Magnificent Seven" tech stocks came to represent over 30% of the S&P 500's market capitalization. Shiller's framework helps distinguish between genuine technological transformation and the speculative excess that often accompanies it.
Demographic patterns: Baby boomers entering peak saving years in the 1990s increased stock market demand. This created structural upward pressure on prices, but investors mistook a demographic tailwind for fundamental value creation.
Favorable monetary policy: Low interest rates reduce the cost of capital, rationally supporting higher P/E ratios. But investors often extrapolate monetary conditions indefinitely and price assets as if permanently low rates are guaranteed.
Feedback loops:
Prices rise
→ Investors earn high returns
→ More investors enter the market
→ Demand increases further
→ Prices rise more
→ Stories about riches spread
→ Even more investors enter
→ Prices reach unsustainable levels
→ Eventual correctionThis positive feedback loop is the engine of every bubble. Shiller traces it through the 1920s stock boom, the 1980s Japanese asset bubble, the 1990s tech bubble, and the 2000s housing bubble. The pattern repeats with remarkable consistency. For a deeper look at how investor psychology drives these cycles, read our guide to the fear of investing.
Media amplification: Financial media profit from covering rising markets. Stories about people getting rich attract readers. The media both reflects and amplifies the feedback loop, providing the "new era" narrative that makes each bubble feel justified.
Shiller integrates behavioral finance throughout:
One of Shiller's most interesting sections addresses the cultural transmission of investment ideas:
Shiller borrows from epidemiology to model how investment ideas spread through populations. A good investment story spreads like a virus: it infects a host (investor), replicates (investor tells friends), and spreads to new hosts.
The most effective investment narratives:
Historical investment narratives:
| Era | Narrative | Result |
|---|---|---|
| 1920s | "Stocks provide permanent prosperity" | 1929 crash |
| 1960s | "The Nifty Fifty always grows" | 1973-74 crash |
| 1990s | "Internet changes everything about valuation" | 2000 crash |
| 2000s | "Real estate only goes up" | 2008 crash |
| 2020-21 | "TINA: There Is No Alternative to stocks" | 2022 correction |
| 2024-26 | "AI changes everything about valuation" | TBD |
Shiller does not recommend trying to time the market based on CAPE. He recommends using it to calibrate return expectations and asset allocation:
At very high CAPE (above 30):
With the CAPE at approximately 41 in July 2026, this is the most relevant scenario for today's investors. I used Shiller's framework in early 2025 to adjust my own expectations. Instead of assuming the historical 10% nominal return from U.S. equities, I built my retirement plan around 5-6% nominal returns. I also increased my international equity allocation from 20% to 35%, since international markets trade at significantly lower CAPE ratios. I did not sell my U.S. holdings, but I stopped adding to them at the same rate. Whether this turns out to be the right call remains to be seen, but the point is that Shiller's framework gave me a rational basis for the decision rather than a gut feeling.
At very low CAPE (below 15):
At average CAPE (15-25):
One of Shiller's most actionable insights: international equity markets often have significantly different CAPE ratios. Investors who diversify globally can find better-valued markets:
International CAPE Comparison (approximate, July 2026):
| Market | CAPE (approx.) | Implied Expected Return |
|---|---|---|
| U.S. (S&P 500) | 38-41 | Low (1-3% real) |
| UK (FTSE) | 13-16 | Medium-High |
| Europe (Stoxx) | 15-18 | Medium-High |
| Japan (Nikkei) | 22-27 | Medium |
| Emerging Markets | 13-17 | Medium-High |
This suggests international diversification is not just about reducing correlation risk. It is also about accessing more attractively valued markets. For a practical guide to this approach, see our article on dollar-cost averaging.
The second edition, published in 2005, added prescient analysis of the U.S. housing market. Shiller's key finding: real home prices had been essentially flat from 1890 to 1997, with values rising only with inflation. The surge from 1997 to 2005 was historically unprecedented and not explained by any fundamental driver.
Real U.S. Home Price Index (Shiller, base year 1890=100):
| Year | Index |
|---|---|
| 1890 | 100 |
| 1950 | 110 |
| 1997 | 110 |
| 2006 (peak) | 199 |
| 2012 (trough) | 134 |
| 2022 | 220+ |
| 2025 | 235+ |
The 2025 figure shows another historically unusual run-up in real home prices. Shiller has commented on this in recent interviews, noting that while housing supply constraints and remote work patterns explain some of the increase, the magnitude of the price rise relative to long-term historical norms is concerning. For a practical tool to evaluate housing decisions, see our rent vs buy calculator.
Q: Does high CAPE mean I should sell stocks now?
A: No. Shiller himself maintains significant equity exposure despite high CAPE. High CAPE indicates lower expected future returns and higher probability of significant drawdowns, not a certain near-term crash. Use it to calibrate expectations and allocation, not as a timing signal.
Q: Is CAPE available for free?
A: Yes. Shiller publishes monthly CAPE data free on his Yale website (econ.yale.edu/~shiller/data.htm). It is updated monthly.
Q: How should I use CAPE practically?
A: As a long-run return calibration tool. If you are 10 years from retirement and CAPE is at 41 (as it is in July 2026), your expected 10-year nominal return from U.S. equities is probably 3-5%, not the historical 10%. Plan accordingly. Save more, spend less in retirement, or diversify into international equities with lower CAPE. Use our retirement calculator to model different return scenarios.
Rating: 4.6/5
Irrational Exuberance is the most important book on market valuation written in the last 25 years. The CAPE ratio alone justifies reading it. The bubble anatomy, historical data, and behavioral context make it essential for any investor trying to understand the relationship between current market prices and long-run expected returns. With the CAPE ratio at approximately 41 in July 2026, near the dot-com peak levels, Shiller's framework is more relevant than it has been in two decades.
Paperback: Buy on Amazon
Kindle: Buy on Amazon
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For more on market valuation and investing strategy, read our guide to dollar-cost averaging and what is an index fund.
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