Cape Ratio
The Cape Ratio (Cyclically Adjusted Price-to-Earnings Ratio) is a valuation metric that divides a stock's current price by its average inflation-adjusted earnings over the past 10 years. Originally proposed by Yale economist Robert Shiller, it smooths out the wild swings of the traditional P/E ratio by accounting for an entire business cycle, giving investors a clearer picture of whether a market is genuinely overvalued or undervalued.
Short Definition
The Cape Ratio (Cyclically Adjusted Price-to-Earnings Ratio) is a valuation metric that divides a stock's current price by its average inflation-adjusted earnings over the past 10 years. Originally proposed by Yale economist Robert Shiller, it smooths out the wild swings of the traditional P/E ratio by accounting for an entire business cycle, giving investors a clearer picture of whether a market is genuinely overvalued or undervalued.
What It Is
Unlike a standard P/E ratio, which uses just the last 12 months of earnings, the Cape Ratio stretches its earnings window across a full decade. The idea is simple but powerful: corporate profits are cyclical. A company might look cheap on a P/E basis during a boom year when earnings spike, or expensive during a recession when profits temporarily collapse. By averaging earnings over 10 years and adjusting each year's figure for inflation using the Consumer Price Index (CPI), the Cape Ratio filters out those cyclical distortions and reveals the underlying earning power of a company or index.
The ratio gained widespread attention after Robert Shiller used it to warn of the dot-com bubble in the late 1990s. At the peak of that bubble in December 1999, the S&P 500's Cape Ratio hit approximately 44 — a level never before recorded in U.S. market history. For context, the long-term median Cape Ratio for the S&P 500 since 1881 is roughly 17. When the ratio has climbed above 30, major market corrections have typically followed. After the 2008 financial crisis, the ratio dipped below 13 in early 2009, signaling what turned out to be one of the greatest buying opportunities of the century.
Today, the Cape Ratio is most commonly applied to broad market indices rather than individual stocks, because the 10-year smoothing technique works best when applied to large, diversified earnings pools. As of mid-2025, the S&P 500's Cape Ratio has hovered in the range of 35 to 38, well above historical norms and second only to the dot-com era peak. This has sparked intense debate among analysts about whether the ratio still works in an economy dominated by high-margin technology companies.
How It Works
Calculating the Cape Ratio involves three straightforward steps. First, you take the current price of the stock or index. Second, you collect the earnings per share (EPS) for each of the past 10 years and adjust each year's earnings for inflation to express them in today's dollars using the CPI. Third, you sum those 10 inflation-adjusted earnings figures and divide by 10 to get the average. Finally, you divide the current price by that 10-year average. The formula looks like this: Cape Ratio = Current Price ÷ Average of 10 Years of Inflation-Adjusted Earnings.
For example, if the S&P 500 is trading at 5,500 and the average inflation-adjusted EPS over the past decade is $150, the Cape Ratio would be 36.7 (5,500 ÷ 150). Compare that to a traditional P/E of, say, 22 based on the most recent year's earnings of $250 — the Cape Ratio tells a very different story about valuation. The gap between the two numbers often signals that current earnings are running well above their long-term trend, which could mean mean reversion is ahead.
Investors and analysts typically track the Cape Ratio over time rather than treating any single reading as a buy or sell signal. A ratio significantly above the historical median of 17 suggests the market is expensive and future returns may be subdued. A ratio below 15 has historically preceded periods of strong long-term returns. Shiller's research found that when the Cape Ratio was in the top quintile (above roughly 25), subsequent 10-year real returns averaged near zero or even turned negative.
Practical Example
Imagine it's January 2025 and you're evaluating whether to invest a $50,000 lump sum into an S&P 500 index fund. The index is trading at 5,800. The most recent annual EPS is $260, giving a traditional P/E of about 22.3 — which looks reasonable by recent standards. But when you calculate the Cape Ratio, you find that the 10-year average inflation-adjusted EPS is $155, yielding a Cape Ratio of 37.4. That's higher than 95% of all readings since 1881.
Looking at history, you see that the only time the ratio was comparably elevated was in 1999, and the S&P 500 went on to deliver negative real returns over the following decade. Armed with this information, you might decide to dollar-cost average your $50,000 over 12 months rather than investing it all at once, or you might allocate a portion to bonds or international markets where Cape Ratios are lower. This is exactly the kind of disciplined, data-driven decision the Cape Ratio is designed to support.
Why It Matters
The Cape Ratio matters because it forces investors to confront a psychological trap: recency bias. When earnings are booming, the traditional P/E looks attractive, and investors pile in near the top. When earnings crater during a recession, the P/E looks terrifying, and investors sell at the bottom. The Cape Ratio cuts through both illusions by anchoring valuation to a decade of smoothed, inflation-adjusted data. For long-term investors with time horizons of 10 years or more, it provides one of the most reliable predictors of future real returns available.
Beyond individual decision-making, the Cape Ratio shapes institutional strategy. Pension funds, endowments, and sovereign wealth funds use it to set strategic asset allocations. When the ratio is elevated, these institutions often shift toward alternative assets, bonds, or international equities. The ratio also influences academic finance — Shiller's work on the Cape Ratio contributed to his 2013 Nobel Prize in Economics, lending it significant credibility in both academic and practitioner circles.
Limitations and Risks
The Cape Ratio is not without serious critics. One major limitation is that accounting standards change over time. The way companies recognize revenue, depreciate assets, and report pension obligations has shifted dramatically over the past decade, meaning that year-one earnings from 2015 may not be directly comparable to year-ten earnings from 2025. This can distort the 10-year average in ways that make the ratio either too high or too low relative to true economic earnings.
Another risk is structural change in the economy. The S&P 500 today is dominated by technology and healthcare companies with far higher profit margins than the industrial and commodity firms that dominated the index in earlier decades. Critics like Jeremy Siegel argue that higher margins are partly justified by business model evolution, making the Cape Ratio look artificially elevated. Additionally, the ratio is a poor timing tool — it can stay elevated for years (as it did from 1995 to 2001) before a correction arrives, meaning an investor who acts on a high Cape Ratio signal too early can miss significant gains or suffer opportunity costs in a rising market.
FAQ
What is a "good" Cape Ratio?
There is no single magic number, but historical context helps. A Cape Ratio between 15 and 20 has historically been associated with healthy long-term forward returns averaging 6% to 8% annually after inflation. Ratios above 30 have historically preceded periods of flat or negative real returns over the following decade. The key is to compare the current reading to the long-term median of approximately 17.
Can I use the Cape Ratio for individual stocks?
It's possible but less reliable. Individual companies can experience permanent shifts in their business models, go bankrupt, or be acquired — all of which make a 10-year earnings average misleading. The Cape Ratio works best on broad, stable indices like the S&P 500 or the MSCI World Index where the composition changes slowly and earnings are diversified across hundreds of companies.
Where can I find the current Cape Ratio for the S&P 500?
Robert Shiller publishes updated data on his website at www.econ.yale.edu/~shiller/data.htm, including monthly S&P 500 Cape Ratio figures going back to 1881. Several financial data platforms like GuruFocus, Multpl.com, and Star Capital also publish the ratio with regular updates and historical charts.
Bottom Line
The Cape Ratio is one of the most battle-tested valuation tools in finance, and its core message is timeless: paying a high price relative to long-term earning power rarely ends well for patient investors. While it shouldn't be your only metric — structural economic changes, accounting shifts, and its poor short-term timing ability all demand caution — it remains an essential reality check against market euphoria. Use it as a compass, not a clock: it won't tell you exactly when to buy or sell, but it will tell you whether you're sailing into dangerous waters or calm seas.
Which related MoneyBestPal guides should you read?
Use this topic as part of a wider finance toolkit. Related areas to review include:
Educational disclaimer: This MoneyBestPal article is for general financial education only. It is not investment, tax, legal, or accounting advice. Consider speaking with a qualified professional before making decisions based on your personal situation.
