As of July 2026, the Shiller CAPE ratio for the S&P 500 stood at around 41x, more than double its long-run historical median of roughly 17x, a level that has been reached only a handful of times since the data series began in 1881, most notably just before the 1929 crash and around the dot-com peak in 1999-2000. Numbers like this get quoted often in market commentary, but the CAPE ratio itself is frequently misunderstood, either dismissed as an academic curiosity or misused as a short-term timing signal it was never designed to be. This piece breaks down what the CAPE ratio actually measures, how it differs from the P/E ratio most investors already know, how to use it sensibly, and where its real limitations lie.
What Is the CAPE Ratio?
The CAPE ratio, short for Cyclically Adjusted Price-to-Earnings ratio, is a long-term stock market valuation measure that compares a stock index’s price to its average inflation-adjusted earnings over the preceding ten years, rather than to a single year of earnings the way a conventional P/E ratio does. It is also widely known as the Shiller P/E ratio, or sometimes “P/E10” or the “Campbell-Shiller PE,” after the two economists who formalised it. The core idea is straightforward: a single year of corporate earnings can be unusually high during an economic boom or unusually depressed during a recession, and either extreme distorts a standard P/E ratio into showing a valuation snapshot that doesn’t reflect the market’s sustainable, cycle-adjusted worth. By averaging earnings across a full decade, typically enough time to span at least one recession and one expansion, the CAPE ratio aims to reflect something closer to a company’s or an index’s normalised earning power, smoothing over the noise of any single year.
Who Created the CAPE Ratio?
The CAPE ratio was formally introduced in a 1988 academic paper by Yale economist Robert J. Shiller and his then-doctoral student, John Y. Campbell, though the underlying idea traces back further, to Benjamin Graham and David Dodd’s foundational 1930s work on security analysis, which had already suggested averaging earnings over several years to smooth out cyclical distortions. Shiller later popularised the concept for a mainstream audience in his 2000 book “Irrational Exuberance,” published just as the dot-com bubble was peaking, a work now regarded as a prescient warning about stretched valuations. Shiller, a professor at Yale University, went on to win the Nobel Memorial Prize in Economic Sciences in 2013, awarded jointly with Eugene Fama and Lars Peter Hansen, in part for his empirical work on asset price predictability, of which the CAPE ratio is one of his best-known contributions. He is also known for co-developing the Case-Shiller home price index and for his broader body of work challenging the strict form of the Efficient Market Hypothesis.
How Is the CAPE Ratio Calculated?
The formula for the CAPE ratio is:
CAPE Ratio = Real (Inflation-Adjusted) Price / 10-Year Average of Real (Inflation-Adjusted) Earnings Per Share
In practice, this involves a few steps. First, the current price of the index or stock is taken as-is, since it already reflects today’s rupee or dollar value. Second, the earnings per share for each of the preceding ten years is individually adjusted for inflation, typically using a consumer price index, so that a rupee of earnings from ten years ago is restated in today’s purchasing-power terms rather than compared directly to nominal figures from a decade with very different price levels. Third, these ten inflation-adjusted annual EPS figures are averaged into a single number, commonly referred to as “E10.” Finally, the current real price is divided by this E10 figure to arrive at the CAPE ratio. For example, if a market index is trading at 6,000 points and its real, inflation-adjusted average EPS over the past ten years works out to 145, the CAPE ratio would be approximately 6,000 ÷ 145, or about 41.4, broadly in line with where the S&P 500’s Shiller CAPE stood in mid-2026. Robert Shiller has maintained and published this dataset for the US market going back to 1881 on his own Yale data page, and similar CAPE datasets have since been constructed for other markets, including India, where the IIM Ahmedabad CAPE India data resource calculates the ratio using BSE Sensex and Nifty 500 data across 10-year, 7-year, and 5-year business-cycle variants.
Why the CAPE Ratio Is Different from the Traditional P/E Ratio
| Aspect | Traditional P/E Ratio | CAPE Ratio (Shiller P/E) |
| Earnings period used | Most recent single year (trailing twelve months) or forward estimate | Average of the past 10 years |
| Inflation adjustment | Not applied | Both price and each year’s earnings adjusted to real terms |
| Sensitivity to the business cycle | High; can look artificially cheap at earnings peaks and artificially expensive at earnings troughs | Lower; averaging smooths out boom-and-bust earnings swings |
| Best suited for | Short-term or company-specific valuation snapshots | Long-term, cycle-adjusted valuation of broad market indices |
| Predictive power for near-term (1-year) returns | Limited, similar to CAPE | Also limited; not designed for short-term timing |
| Predictive power for long-term (10-year) returns | Weak | Historically stronger; Shiller and Campbell’s original research found CAPE explained a meaningful share of the variance in subsequent 10-year real returns |
| Data requirement | One year of earnings data | A full decade of earnings history, which can be a constraint for newer companies or newer markets |
The practical difference shows up most clearly at economic turning points. During a recession, corporate earnings can fall sharply, which mechanically inflates a standard trailing P/E ratio even if the stock price hasn’t moved much, making the market look expensive exactly when it may actually be cheap. Conversely, at the peak of an economic boom, unusually high earnings can make the standard P/E ratio look deceptively low. The CAPE ratio’s ten-year averaging window is specifically designed to reduce this distortion, which is why it is generally treated as a longer-horizon complement to the standard P/E ratio rather than a replacement for it.
How to Use the CAPE Ratio
The CAPE ratio is best treated as a long-horizon valuation gauge rather than a short-term trading signal. Academic research following Shiller and Campbell’s original work has found that the correlation between starting CAPE levels and subsequent ten-year real returns has historically been strong, with some studies citing a correlation coefficient in the region of -0.75, meaning that unusually high CAPE readings have tended to precede below-average real returns over the following decade, and unusually low readings have tended to precede above-average ones. At the same time, this same body of research consistently shows that CAPE has almost no meaningful predictive power for returns over the next one or two years; a high CAPE reading does not mean a crash is imminent, and markets can remain expensive by this measure for years. A commonly cited illustration is that the US CAPE ratio first crossed its 1929 pre-crash level back in 1996, a full four years before the dot-com peak in 2000.
Suggested Read: The 2008 Global Financial Crisis
Given this, investors typically use the CAPE ratio in three practical ways. First, as an input into asset allocation decisions, tilting a long-term portfolio toward higher or lower equity exposure based on whether a market’s CAPE sits meaningfully above or below its own long-run historical median, rather than trying to time an exact entry or exit point. Second, as a cross-market or cross-country comparison tool, since Shiller’s methodology has been extended to markets beyond the US, allowing investors to compare how richly or cheaply different equity markets are priced on a like-for-like, cycle-adjusted basis. Third, as a sense check against short-term valuation narratives, since a stock or index that looks “cheap” on a single year’s earnings may look considerably more expensive once viewed across a full business cycle, and vice versa. It is generally applied to broad market indices rather than individual, especially cyclical, single stocks, since ten full years of comparable earnings history is not always available or meaningful for younger or fast-changing companies.
Advantages of the CAPE Ratio
The CAPE ratio’s central advantage is that it smooths out the distortion a single unusual year of earnings can cause, offering a more stable view of an index’s underlying valuation across a full economic cycle rather than at one potentially misleading point in time. Because it explicitly adjusts both price and earnings for inflation, it also allows for more meaningful comparisons across different time periods and different inflationary environments, something a simple nominal P/E ratio cannot do reliably. Historically, and this is the finding that underpinned part of Shiller’s Nobel citation, CAPE levels have shown a materially stronger empirical relationship with long-run (ten-year) real returns than conventional valuation measures, making it a genuinely useful tool for investors thinking in decades rather than quarters. It is also flexible enough to be applied across different equity markets, letting analysts compare, for instance, how the US market’s valuation stacks up against other major markets on a consistent, cycle-adjusted basis, which is part of why researchers have built parallel CAPE datasets for markets including India.
Limitations of the CAPE Ratio
Despite its strengths, the CAPE ratio has well-documented limitations that any investor using it should keep in mind. Its predictive power is almost entirely a long-horizon phenomenon; used as a short-term timing tool, it performs poorly, and investors who have exited equities purely because CAPE looked “too high” have, at various points in history, missed years of subsequent gains before any eventual reversion. The ratio can also be distorted by structural shifts in corporate behaviour over long stretches of time: accounting standards have changed materially over the decades covered by Shiller’s dataset, affecting how comparably “earnings” are measured across different eras, and the growing preference among (particularly US) companies for share buybacks over dividends, a shift that reduces the share count and mechanically boosts EPS, has led Shiller himself to publish a refined variant, the Total Return CAPE (TR-CAPE), to correct for this effect. A further, frequently raised criticism is that standard CAPE does not account for the prevailing interest rate environment; some analysts argue equity valuations should be judged relative to bond yields at the time, since a higher CAPE may be more justifiable when interest rates are low than when they are high, a critique that has led to refinements such as comparing CAPE-derived earnings yields against real bond yields (an “excess CAPE yield” measure). Data availability is another practical constraint, since a full, reliable ten-year earnings history not distorted by one-off events is not always available, particularly for newer or fast-evolving markets and sectors; India’s own CAPE datasets, for instance, are a comparatively recent academic construction and continue to be refined across different business-cycle-length variants. Finally, CAPE is best applied to broad, diversified indices rather than to individual, especially cyclical or newly listed, stocks, where a decade of comparable per-share earnings may simply not exist or may not represent the same underlying business.
Conclusion
The CAPE ratio doesn’t tell you what the market will do next month, and it was never designed to. What it does offer, reasonably reliably based on more than a century of data, is a cycle-smoothed read on whether a market is expensive or cheap relative to its own long-run history, an input best used for long-term asset allocation rather than short-term trading decisions. Used alongside other valuation tools, and with its known limitations in mind, it remains one of the more empirically grounded valuation frameworks available to long-term investors.
For readers who want to go deeper into valuation frameworks like this one, Elearnmarkets’ structured courses on fundamental analysis and equity valuation work through concepts like CAPE, P/E, and PEG ratios in more depth, with practical, India-specific examples.
FAQs
1. What is considered a high CAPE Ratio?
There’s no single universal cutoff, but readings meaningfully above a market’s own long-run historical median are generally considered elevated. For the US market, the long-run median CAPE since 1881 is roughly 17x; readings sustained above 30x have historically been rare and have clustered around major valuation peaks, including 1929 (32.6x) and the December 1999 dot-com top (44.2x, the record reading in Shiller’s dataset). What counts as “high” should always be assessed relative to that specific market’s own historical range rather than an absolute number applied universally across markets.
2. Can the CAPE Ratio predict market crashes?
Not reliably, and this is one of the most common misunderstandings about the metric. CAPE has historically shown a meaningful statistical relationship with subsequent ten-year real returns, but it has almost no demonstrated power to predict the timing of a crash or correction over the next year or two. Markets have stayed at historically elevated CAPE levels for extended periods before any correction; the US CAPE first crossed its 1929 level in 1996, a full four years before the market actually peaked in 2000. A high CAPE reading is better read as a signal of stretched long-term valuation than as an imminent-crash warning.
3. What is Shiller PE Ratio?
Shiller PE ratio is simply another name for the CAPE ratio, named after Robert Shiller, the Yale economist who popularised it. It is also sometimes referred to as “P/E10” (reflecting its 10-year earnings averaging window) or the “Campbell-Shiller PE,” acknowledging Shiller’s co-author John Campbell. All these terms refer to the same underlying calculation: current inflation-adjusted price divided by the 10-year average of inflation-adjusted earnings per share.
