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Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →The Shiller CAPE ratio is a way to put stock-market valuations in a long historical context. It compares prices with inflation-adjusted earnings averaged over about ten years, so one unusually strong or weak earnings year has less influence than it would on a conventional one-year price-to-earnings ratio. Historical research suggests valuation ratios can help describe the conditions for stock price changes over long horizons. It does not show when a crash will happen, reliably forecast the next year, or tell you what earnings and dividends will do.
What does the Shiller CAPE ratio tell you about future stock returns?
CAPE is most useful as a broad measure of how much investors are paying for a long-run stream of corporate earnings. A higher ratio means market prices are high relative to the smoothed earnings measure; a lower ratio means prices are lower relative to it. That comparison can help frame expectations over long periods, but it is not a return forecast with a dependable date or a specific outcome attached.
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The distinction between price changes and an investor’s total return matters. In their 2001 study, John Y. Campbell and Robert J. Shiller found that valuation ratios appeared useful mainly for forecasting future stock price changes. The study did not find that the ratios reliably forecast future dividend growth, earnings growth, or productivity growth. A stock investor’s realized return can also include dividends, so a finding about price changes should not be treated as a precise prediction of total return. Campbell and Shiller, “Valuation Ratios and the Long-Run Stock Market Outlook: An Update”.
In practical terms, CAPE offers context for thinking about long-run conditions, not a promise that a particular valuation will produce a particular result. It cannot identify the fundamental cause of a future price change, or tell an investor exactly when that change will occur.
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How is CAPE calculated?
CAPE stands for cyclically adjusted price-to-earnings ratio. It relates an equity price measure to a long historical average of inflation-adjusted earnings, commonly using a ten-year earnings window. Adjusting earnings for inflation makes figures from different years more comparable; averaging them reduces the influence of a temporary boom, recession, or other unusually strong or weak earnings period.
A conventional trailing P/E generally compares current price with earnings over a recent one-year period. That makes it more responsive to current earnings, but also more exposed to an unusual year. CAPE smooths the earnings side across a longer period. It is still a ratio, not a complete valuation model: it does not independently account for every factor that can affect what investors will pay for future profits.
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| Measure | Earnings basis | What to keep in mind |
|---|---|---|
| Shiller CAPE | Long-run average of inflation-adjusted earnings, commonly ten years | Smoothing reduces the impact of a single unusual year, but makes the measure reflect a longer history. |
| One-year trailing P/E | Recent historical earnings, typically one year | More directly tied to recent earnings; a single unusually high or low year can have a larger effect. |
| Forward P/E | Expected future earnings | Depends on earnings forecasts and their assumptions. The evidence cited here does not establish that it predicts better or worse than CAPE. |
These measures answer related but different questions. CAPE emphasizes a longer earnings record; trailing P/E emphasizes recent reported earnings; forward P/E uses estimates. None should be read as a standalone verdict on whether the market is fairly priced or where it will go next.
What historical evidence supports using CAPE?
Campbell and Shiller examined aggregate annual U.S. data from 1871 through 2000 and quarterly data for twelve countries beginning in 1970. In that analysis, valuation ratios did poorly at forecasting future dividend growth, earnings growth, and productivity growth. They appeared more useful for forecasting future stock price changes. The finding supports using valuation as one input into a long-horizon outlook, while cautioning against treating it as a forecast of the business fundamentals that will generate returns. The paper’s abstract and publication details.
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The result is not a guarantee that the relationship will hold in the same way in every future period. The study reports historical samples, not a reliable return number for an individual investor or a specific date. The available evidence also does not provide a standalone predictive-performance statistic to turn CAPE into a precise forecast.
Vanguard describes CAPE as a common measure of U.S. equity valuation and valuations as a strong indicator of long-term equity returns. It also notes that lower interest rates can reduce discount rates and affect how much investors are willing to pay for future earnings. That context helps explain why an elevated valuation alone does not prove that investors are irrational: the assumptions and conditions behind the valuation matter. This is explanatory context, not a universal rule or a guarantee. Vanguard, “Reasons for caution about U.S. equity valuations”.
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What data underlies the historical CAPE series?
Robert Shiller’s Yale data page provides monthly U.S. stock prices, dividends, earnings, and consumer price index data beginning in January 1871. Shiller notes that monthly dividend and earnings figures from 1926 onward are derived from quarterly S&P totals; earlier data draw on historical sources and interpolation. The long record is useful for historical comparisons, but the construction and source material are not identical across every part of the series. Shiller’s Online Data page.
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The same page offers an alternative CAPE version and warns that changes in corporate payout policy can affect the ratio. In particular, companies have increasingly used share repurchases rather than dividends. Because payout methods can change earnings per share and how corporate cash reaches shareholders, a CAPE reading can be affected by structural changes as well as by market prices and earnings cycles. This is one reason to be cautious about treating a single historical threshold as a timeless rule.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why can interest rates and market structure change the interpretation?
A valuation ratio compares price with an earnings measure, but the market’s willingness to pay for future earnings also depends on the financial setting. Discount rates are one part of that setting: when rates are lower, the present value investors assign to future cash flows can rise, all else equal. Vanguard’s discussion of rates and U.S. equity valuations provides this context, but it does not establish a formula that converts a rate change into a dependable CAPE level or market return.
Market structure matters too. Changes in how companies distribute cash—including a greater role for repurchases relative to dividends—can affect the earnings-per-share information reflected in the ratio. A historical comparison may therefore mix valuation differences with changes in corporate practices. These considerations complicate interpretation; they do not make CAPE useless or automatically invalidate long-run data.
Can the CAPE ratio predict a stock market crash?
No. The cited evidence does not establish CAPE as a crash-timing signal. A high reading does not tell you when a correction will begin, how large it will be, or whether one is imminent. Valuations can remain elevated for extended periods, just as low valuations can persist. The evidence concerns longer-horizon forecasting, not the timing of next month’s or next year’s market move.
Nor does a high CAPE prove that a crash must follow. It describes a relationship between price and smoothed earnings; it does not identify a trigger or a timetable. Treating it as an instruction to sell can turn a long-term context measure into a short-term bet that the historical evidence does not support.
How should an investor use CAPE without overreading it?
- Check what the ratio measures. Confirm that you are looking at a price-to-smoothed, inflation-adjusted earnings comparison, rather than assuming it is a direct measure of total return or intrinsic value.
- Match the horizon to the evidence. Use CAPE as long-run valuation context. Do not infer a precise monthly or annual return from the cited studies.
- Separate valuation from fundamentals. The cited Campbell and Shiller analysis found valuation ratios more useful for future price changes than for forecasting earnings, dividends, or productivity growth. Do not assume a high or low ratio tells you which of those fundamentals will change.
- Consider the setting. Interest rates, earnings conditions, and payout practices can affect the interpretation. A comparison across distant periods may not be like-for-like if corporate practices have changed.
- Use more than one input. A valuation measure can inform a long-term view, but it should not serve as a standalone reason to predict a crash or make a precisely timed investment decision.
This approach keeps CAPE in its proper role: a way to organize a long-run valuation question, not a signal that removes uncertainty. The historical U.S. record is extensive, and the multi-country study broadens the evidence, but neither guarantees that future markets will behave identically.
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What CAPE cannot tell you
- When a market decline will start. The cited work does not validate CAPE as a crash or correction timer.
- Your next month’s or year’s return. Its evidence concerns long-run relationships rather than dependable short-horizon forecasts.
- Whether earnings or dividends will grow. In the cited study, valuation ratios did poorly at forecasting dividend growth, earnings growth, and productivity growth.
- The one objectively correct fair value. Interest rates, payout policy, and the market environment affect how a valuation should be interpreted.
- A guaranteed future investor experience. A historical association is not certainty about the returns any investor will receive.
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