Understanding the Shiller CAPE Ratio: A Guide to Valuing the Stock Market for Long-Term Investors

November 18, 2025

Learn how Nobel Prize-winning economist Robert Shiller's CAPE ratio helps investors evaluate stock market valuations, understand long-term return expectations, and make informed investment decisions using 10-year cyclically adjusted earnings.

Understanding whether the stock market is expensive or cheap seems straightforward—just compare today's prices to earnings—but anyone who's tried knows it's far more complicated than that. Earnings fluctuate wildly year to year due to economic cycles, recessions, one-off events, and accounting changes, making simple price-to-earnings ratios unreliable for assessing true value. This is where Nobel Prize-winning economist Robert Shiller's Cyclically Adjusted Price-to-Earnings (CAPE) ratio comes in, smoothing out short-term noise to provide a clearer view of long-term stock market valuation.

This guide explains what the CAPE ratio is, how it works, its historical track record in identifying expensive and cheap markets, why it sometimes "doesn't work" in the short term, and most importantly, how investors should actually use it—not as a crystal ball for timing the market, but as one valuable tool among many for setting realistic long-term return expectations.

The challenge of value investing: Why determining "cheap" is harder than it looks

Value investing—the strategy of buying assets trading below their intrinsic worth—sounds simple in principle. Find companies whose share prices don't reflect their true fundamental value, buy them whilst they're undervalued, and wait for the market to eventually recognise their worth. Legendary investors like Warren Buffett built fortunes on this approach, seeking businesses with strong fundamentals trading at bargain prices.

However, determining what constitutes "cheap" or "expensive" is profoundly difficult in practice. A company trading at 10 times earnings might seem like a bargain compared to another at 30 times earnings, but what if the cheaper company faces declining markets, obsolete products, or accounting scandals? Sometimes shares are "cheap for a reason"—the market has already priced in their deteriorating prospects. Even Warren Buffett, perhaps the most successful value investor in history, has made high-profile mistakes buying companies that appeared cheap but turned out to be value traps.

This subjectivity extends to entire stock markets. Is the FTSE 100 expensive or cheap today? Compared to what—last year's prices, earnings, dividends, interest rates, historical averages? Individual investor judgment varies wildly, leading to conflicting conclusions about the same data. This is why investors continuously search for more objective, data-driven valuation metrics that remove some of the guesswork and emotional bias from assessing market value.

What is the Shiller CAPE ratio?

The Cyclically Adjusted Price-to-Earnings ratio, commonly called the CAPE ratio or Shiller PE, was developed by American economist Robert Shiller, who won the Nobel Prize in Economics in 2013 for his empirical analysis of asset prices. The CAPE ratio measures stock market valuation by comparing current prices to average inflation-adjusted earnings over the previous 10 years.

How CAPE differs from traditional PE ratios

Traditional PE (price-to-earnings) ratios divide current share price by the most recent year's earnings per share. Whilst simple to calculate, this creates problems: corporate earnings are volatile, swinging dramatically during recessions (collapsing earnings make PE ratios soar even if prices fall) and economic booms (surging earnings make PE ratios look artificially low). A single year's earnings might be distorted by one-off events—restructuring charges, asset sales, tax changes, or pandemic impacts—that don't reflect normal earning power.

The CAPE ratio solves this by using 10 years of earnings instead of just one year, and adjusting all historical earnings for inflation to make them comparable to today's prices. This 10-year smoothing removes much of the noise from economic cycles, one-off events, temporary recessions or booms, providing a more stable, reliable measure of whether markets are expensive or cheap relative to their long-term earnings capacity.

The basic interpretation: What CAPE numbers mean

CAPE ratio interpretation follows straightforward logic:

Higher CAPE ratios indicate markets are more expensive—investors are paying more per pound of long-term earnings. When CAPE is elevated (significantly above historical averages), it suggests future long-term returns are likely to be lower than normal, as markets are already pricing in optimistic expectations.

Lower CAPE ratios suggest markets are cheaper—investors are paying less per pound of long-term earnings. When CAPE is depressed (significantly below historical averages), it indicates future long-term returns are likely to be higher than normal, as markets are pessimistic and undervaluing earning power.

Crucially, CAPE is not designed to predict short-term market movements or identify exact market tops and bottoms. Instead, it helps assess whether current valuations are likely to support strong or weak long-term returns over the next 7-10 years. Think of it as a thermometer measuring market "temperature" rather than a stopwatch telling you precisely when to buy or sell.

Historical context: When CAPE worked brilliantly

The CAPE ratio gained widespread attention for correctly highlighting extreme valuations before major market bubbles and subsequent corrections.

The late-1990s dot-com bubble

Perhaps CAPE's most famous success was flagging the late-1990s US stock market bubble. By 1999-2000, the S&P 500's CAPE ratio reached approximately 44—the highest level in recorded history at that time, nearly triple its long-term average of around 16-17. Robert Shiller famously warned that such extreme valuations made poor long-term returns highly probable, regardless of short-term momentum.

The market ignored these warnings initially, with the NASDAQ continuing to soar into early 2000. However, the subsequent dot-com crash saw the S&P 500 fall over 40% from peak to trough between 2000-2002, whilst the tech-heavy NASDAQ plunged nearly 80%. Investors who bought at peak CAPE valuations endured a "lost decade" with minimal or negative returns for 10-12 years. Those who heeded CAPE's warning about extreme valuations either reduced equity exposure or tempered return expectations, avoiding severe disappointment.

The post-financial crisis opportunity

CAPE also identified exceptional value during the 2008-2009 financial crisis. As markets collapsed in panic, the S&P 500's CAPE fell to approximately 13-15 by March 2009—well below its historical average—despite the severe recession. This low CAPE suggested markets had overcorrected, pricing in excessive pessimism about future earnings potential.

Investors who recognised this valuation opportunity and bought during the depths of the crisis enjoyed exceptional subsequent returns. The S&P 500 more than tripled over the following decade, delivering average annual returns exceeding 15%—well above historical norms. CAPE correctly identified that despite enormous short-term uncertainty and fear, long-term valuations were attractive for patient investors.

The 2007-2008 pre-crisis warning

Before the financial crisis, CAPE ratios were elevated though not as extreme as the dot-com bubble—roughly 27-28 in 2007. This suggested markets were expensive and vulnerable, though not at bubble extremes. Whilst CAPE didn't predict the timing or severity of the crisis, it accurately indicated that long-term return prospects were modest at best given elevated valuations. Markets indeed delivered poor returns from 2007 through early 2013, taking six years just to regain 2007 peaks.

When CAPE "didn't work": Important limitations to understand

Despite its historical successes, CAPE has faced sustained criticism for appearing "broken" in recent years, particularly regarding US markets.

The expensive-but-rising US market of the 2010s

One of CAPE's most significant challenges emerged after 2009. US stock market CAPE ratios remained elevated throughout the 2010s—often 25-30 or higher—persistently above historical averages. Traditional CAPE interpretation suggested expensive valuations would lead to poor returns, yet US stocks delivered exceptional gains throughout this period. The S&P 500 more than tripled from 2009-2019 despite "expensive" CAPE ratios the entire time.

Critics argued this proved CAPE was obsolete, unable to account for modern market dynamics. However, this misunderstands CAPE's purpose: it measures long-term valuation, not short-term price direction. Markets can absolutely continue rising from expensive levels—momentum, central bank stimulus, earnings growth, and investor enthusiasm can drive prices higher regardless of starting valuation. CAPE simply suggests that buying at elevated levels reduces expected future returns compared to buying at cheaper valuations.

Structural changes affecting CAPE interpretation

Several structural market changes have potentially shifted "normal" CAPE levels, making historical comparisons less straightforward:

Interest rates: Ultra-low interest rates since the financial crisis make higher equity valuations more justifiable. When bonds yield 0-2%, investors accept lower earnings yields (higher PE ratios) on equities. If low rates persist, structurally higher CAPE ratios may be the "new normal" rather than overvaluation.

Sector composition: The S&P 500 has shifted dramatically toward technology companies with higher margins, less capital intensity, and faster growth than traditional industries. These businesses naturally command higher valuations. Comparing today's tech-heavy CAPE to 1950s manufacturing-heavy CAPE may be misleading.

Accounting standards: Changes in how companies report earnings—particularly regarding intangible assets, research and development, stock-based compensation—can affect reported earnings without changing underlying business economics, potentially distorting CAPE comparisons over long periods.

International CAPE differences

CAPE ratios vary dramatically between countries, yet these differences haven't always translated neatly into return differences. For example, UK and European markets often trade at CAPE ratios of 12-18 whilst US markets sit at 25-35, suggesting foreign markets are cheaper. However, US markets have persistently outperformed despite higher valuations, reflecting stronger economic growth, more dynamic companies, and sector composition differences.

Similarly, Japanese markets traded at extremely low CAPE ratios throughout the 2000s and 2010s following their 1990s bubble collapse, yet delivered disappointing returns despite appearing "cheap." This demonstrates that CAPE, like all valuation metrics, doesn't work in isolation—economic growth, corporate governance, currency movements, and investor sentiment all matter tremendously.

How investors should actually use CAPE: Practical guidance

Given both its successes and limitations, how should investors incorporate CAPE into decision-making?

Set realistic long-term return expectations

CAPE's most valuable use is calibrating return expectations over 7-10 year horizons. When CAPE is high (above historical averages), temper expectations—don't assume the exceptional returns of the past will continue indefinitely. When CAPE is low (below historical averages), recognise you may be buying at attractive long-term valuations despite near-term uncertainty.

For example, buying US equities in late 2021 with CAPE around 38 suggested future returns would likely be below historical 10% averages. This doesn't mean don't invest—it means budget for perhaps 5-7% returns rather than 10-12%, and adjust savings rates or risk allocations accordingly. Conversely, buying in March 2020 with CAPE around 22 suggested more attractive long-term prospects.

Use CAPE as one tool among many, not a timing signal

CAPE should never be used alone to make buy/sell decisions. Markets can remain expensive or cheap for years—the 1990s bubble stayed expensive for nearly five years before correcting. Selling everything because CAPE is high means potentially missing years of gains, whilst buying only when CAPE is low might mean never investing in strong markets.

Instead, combine CAPE with other valuation metrics (dividend yields, price-to-book, forward PE ratios), economic indicators (GDP growth, unemployment, inflation), and personal circumstances (time horizon, risk tolerance, goals). CAPE provides context but shouldn't dictate actions in isolation.

Remember CAPE works better for indices than individual stocks

CAPE was designed for evaluating broad market indices like the S&P 500 or FTSE 100, where 10-year earnings smoothing makes sense. Applying CAPE to individual companies is problematic—businesses change dramatically over 10 years through restructuring, new products, or market disruption, making 10-year averages less meaningful. For individual stock selection, traditional fundamental analysis and shorter-term PE ratios remain more appropriate.

Focus on diversification and long-term investing

Perhaps the most important lesson from CAPE is that market timing is extraordinarily difficult even with sophisticated metrics. Rather than obsessing over whether CAPE is 20 or 30, focus on building diversified portfolios across geographies, sectors, and asset classes, and maintaining discipline through market cycles. Regular investing (pound-cost averaging) naturally buys more at low valuations and less at high valuations without requiring perfect timing.

CAPE is a useful navigation tool on a long journey, helping you understand whether the investment landscape ahead looks favourable or challenging. It's not a GPS telling you exactly when to turn left or right. Use it to inform your strategy and expectations, not to dictate short-term tactical moves.

Frequently asked questions

Is the CAPE ratio reliable?

CAPE is reasonably reliable for its intended purpose—assessing long-term market valuation and setting return expectations over 7-10 year periods—but it's not infallible. It successfully identified extreme over-valuation before the dot-com crash and attractive valuations after the 2008-2009 crisis. However, it can remain elevated or depressed for years whilst markets move against it in the short term. Structural changes (interest rates, sector composition, accounting standards) may have shifted "normal" CAPE levels, making historical comparisons less straightforward. It's reliable as one input among many for long-term planning, but unreliable for short-term market timing.

What is a "good" CAPE ratio?

There's no universally "good" CAPE level—it depends on context. Historically, the US S&P 500's CAPE has averaged around 16-17, so readings below 15 generally suggest attractive valuations whilst readings above 25-30 indicate expensive markets. However, these benchmarks may have shifted: ultra-low interest rates since 2008 arguably justify structurally higher CAPE ratios as investors accept lower earnings yields when bonds yield almost nothing. Rather than focusing on absolute CAPE numbers, compare current levels to recent historical ranges (past 20 years) and consider whether interest rates, economic growth, and sector composition justify deviations from long-term averages. Markets with CAPE well below their own historical averages offer better long-term value than those well above, regardless of absolute numbers.

Does CAPE predict stock market crashes?

No, CAPE does not predict crashes with timing precision. Whilst elevated CAPE ratios indicate markets are expensive and potentially vulnerable to corrections, they don't tell you when corrections will occur. The late-1990s bubble saw CAPE exceed 30 in 1997, yet markets rose another 60%+ before peaking in 2000. Similarly, CAPE was elevated in 2017-2019, yet no crash materialised for several years. High CAPE means lower expected long-term returns and greater vulnerability if sentiment shifts, but markets can remain expensive longer than seems rational. Conversely, low CAPE doesn't guarantee immediate rebounds—Japanese markets stayed cheap for decades. Think of CAPE as measuring vulnerability or opportunity, not predicting specific events or timing.

Is CAPE useful for picking individual stocks?

CAPE is generally not useful for individual stock selection. It was designed for broad market indices where 10-year earnings averaging smooths economic cycles. Individual companies change too dramatically over 10 years—through restructuring, new product launches, management changes, or industry disruption—for 10-year average earnings to meaningfully represent current earning power. A technology company today might be completely different from 10 years ago. For individual stocks, traditional fundamental analysis, shorter-term PE ratios, price-to-sales, cash flow analysis, and competitive positioning are more appropriate. CAPE's value is in assessing overall market or sector valuations, not picking specific shares.

Key takeaways for investors

The Shiller CAPE ratio provides valuable perspective on stock market valuations, particularly for long-term investors trying to set realistic return expectations. Its 10-year earnings smoothing removes much of the noise from economic cycles and one-off events, offering a more stable view of whether markets are expensive or cheap relative to their earning power. Historical track record shows CAPE successfully identified extreme over-valuation before major bubbles and attractive valuations during crisis periods.

However, CAPE is not a market timing tool or crystal ball. Markets can remain expensive or cheap for years whilst delivering strong or weak returns contrary to CAPE signals. Structural changes—interest rates, sector composition, accounting standards—may have shifted "normal" valuation ranges, making direct historical comparisons less reliable. International CAPE differences haven't always translated into predictable return patterns.

The practical takeaway is to use CAPE as one input among many when assessing market valuations and setting long-term return expectations. When CAPE is elevated, moderate your expectations and perhaps tilt toward value regions or defensive sectors. When CAPE is depressed, recognise you may be buying at attractive long-term levels despite near-term uncertainty. But don't let CAPE alone drive buy/sell decisions—combine it with diversification across geographies and sectors, disciplined regular investing, and a long-term time horizon that can ride out inevitable short-term volatility.

Value investing remains as challenging as ever, but tools like the CAPE ratio help remove some of the guesswork and emotional bias, providing data-driven context for making more informed long-term investment decisions.

Author: David Gregory, Financial Planner & Director at Off-Piste Wealth. FCA authorised and regulated. Last reviewed: November 2025. Service areas: Investment management, portfolio construction, market analysis, financial planning, long-term wealth strategies.