The Cyclically Adjusted Price-to-Earnings ratio, known as the CAPE ratio or the Shiller P/E, is among the most robust and most actionable market valuation tools available to long-term investors. Developed by Nobel laureate Robert Shiller at Yale University, the CAPE smooths earnings over ten years to remove the cyclical distortions of individual business cycles, producing a more stable measure of the price investors are paying for each dollar of long-run earnings power.
The historical relationship between the CAPE ratio and subsequent ten-year equity returns is well documented and statistically significant. When the CAPE is low by historical standards, below 15, subsequent ten-year returns have historically been strong. When the CAPE is high, above 25 to 30, subsequent ten-year returns have historically been moderate or poor. The CAPE doesn't predict short-term market movements, and it certainly doesn't predict the exact magnitude or timing of corrections. What it does predict, with meaningful accuracy, is the range of likely returns over a decade-long horizon.
For retirement planning, the CAPE matters because the return sequence in the first decade of retirement has an outsized impact on whether the plan survives. A retiree who begins drawing income from a portfolio at historically elevated valuations faces a higher probability of poor early returns, and poor early returns create sequence of returns risk that can permanently impair an otherwise sound plan. Understanding the CAPE and incorporating it into planning assumptions is one of the most important things a thoughtful retirement planner can do.
The U.S. equity market has spent extended periods in the mid-2020s at CAPE ratios that are elevated by long-run historical standards. The long-run average CAPE ratio going back to 1881 is approximately 17. CAPE ratios in the high twenties and thirties, which have characterized significant portions of recent market history, have historically been followed by lower-than-average ten-year returns rather than the continuation of the returns that produced the elevated ratio.
This is not a prediction of an imminent crash or a signal to exit equities. It is a statement about expected returns. A retiree who plugs a 7% or 8% annual return assumption into their retirement plan at a time when historical relationships between current valuation and forward returns suggest something closer to 4% or 5% is using an overly optimistic assumption. The plan that works at 7% may not work at 4%.
The CAPE ratio divides the current price of the S&P 500 index by the average of the past ten years of inflation-adjusted earnings. The ten-year earnings average removes the impact of individual business cycles, recessions, and recovery periods that distort any single year's earnings figure. A company at the bottom of a recession reports depressed earnings that make the P/E ratio appear high. At the peak of a boom, artificially inflated earnings make the P/E appear low. The CAPE smooths both distortions by averaging across a full business cycle.
The result is a valuation measure that is meaningfully more stable and more predictive than the trailing twelve-month P/E ratio that dominates financial media coverage. The CAPE is updated monthly on Robert Shiller's public data page at Yale and is widely tracked by institutional investors and economic researchers.
Shiller's research documents the relationship between the CAPE ratio and subsequent ten-year real returns on U.S. equities going back to 1881. The relationship is negative, statistically significant, and consistent: higher CAPE ratios are followed by lower ten-year returns, lower CAPE ratios are followed by higher ten-year returns. The predictive power is imperfect, and there are periods where the relationship has been weaker, but no serious critique of the data has overturned the basic finding.
The practical implication is that the CAPE ratio at the beginning of a retirement provides information about the likely return environment for the first decade of that retirement. A retiree beginning at a CAPE of 35 should have a different return assumption in their retirement model than a retiree beginning at a CAPE of 12, because the historical evidence suggests meaningfully different forward return distributions.
Wade Pfau published research in 2011 and subsequent years showing that the safe withdrawal rate is sensitive to the CAPE ratio at the beginning of retirement. His analysis found that retirees who began retirement at historically high CAPE ratios faced lower historically safe withdrawal rates than those who retired at lower valuations. The 4% rule was derived from all historical periods, including those starting at low and moderate valuations. Applied specifically to high-valuation starting points, the historical data suggests a lower sustainable rate.
This finding has practical significance for any retiree using a standard 4% withdrawal rate assumption at a time of elevated CAPE ratios. The conventional assumption may be overly optimistic relative to what the starting valuation environment historically supports.
The CAPE ratio is a poor short-term market timing tool. The relationship between CAPE and subsequent returns operates over ten-year horizons, not one-year or two-year horizons. An elevated CAPE can remain elevated for years or decades before the return normalization occurs. Investors who exited equities when the CAPE was 25 in the early 1990s missed a significant portion of the technology boom before the eventual correction in 2000.
The CAPE also doesn't account for structural changes in the economy or in accounting standards that might justify permanently higher valuations. The shift toward asset-light, high-margin technology businesses, changes in corporate tax rates, and differences in interest rate environments all affect the appropriate P/E level. Critics argue that comparing today's CAPE to nineteenth-century data doesn't adequately account for these structural differences.
Robert Shiller's landmark paper 'Do Stock Prices Move Too Much to Be Justified by Subsequent Changes in Dividends?,' published in 1981 in the American Economic Review, established the empirical foundation for excess market volatility and, implicitly, for mean reversion in market valuations. His subsequent work, particularly the books Irrational Exuberance published in 2000 and Narrative Economics in 2019, extended and popularized these findings for a general audience.
Shiller received the Nobel Prize in Economics in 2013, shared with Eugene Fama and Lars Peter Hansen, for empirical analysis of asset prices. The Nobel committee cited his work on the long-run predictability of asset returns from valuation ratios as among his most significant contributions.
Wade Pfau's research on the interaction between starting valuations and safe withdrawal rates represents the most direct application of Shiller's work to retirement planning. His papers, published in the Journal of Financial Planning between 2011 and 2016, show that the historically safe withdrawal rate varies with the CAPE ratio at the beginning of retirement in a statistically significant way. Retirees starting at high CAPE ratios have historically experienced lower safe withdrawal rates than the aggregate 4% rule suggests.
Pfau's work argues for using a valuation-adjusted withdrawal rate assumption, applying a more conservative starting withdrawal when CAPE is elevated and a more generous one when CAPE is depressed, as a more accurate reflection of the likely forward return environment.
Michael Kitces has written about the implications of long-run market valuation cycles for retirement income planning. His analysis of historical return data shows that returns over thirty-year retirement horizons are less sensitive to starting valuations than ten-year returns, because valuation normalization tends to occur within the first decade and subsequent returns reflect more normal valuations. However, for retirees, it's precisely the first decade that matters most due to sequence of returns risk.
A retirement plan that uses a fixed 7% or 8% annual return assumption regardless of current valuation levels may be systematically overestimating forward returns in high-CAPE environments. Using a range of return assumptions, from optimistic to conservative, and understanding the plan's success rate at the lower end of that range, provides a more complete picture of retirement resilience.
Even without knowing whether current valuations will normalize through a correction or through an extended period of low returns, a retirement plan should be tested against a scenario where equity returns average 3% to 5% real for the first ten years of retirement. If the plan fails this stress test, the retiree should understand that risk and take steps to improve resilience before retirement.
The CAPE ratio is a valuable input into retirement planning but not the only one. Dividend yields, interest rate levels, economic growth trends, and the specific portfolio composition all affect expected returns. The CAPE provides a long-run valuation perspective that should inform but not dominate the planning conversation.
A retiree entering a high-CAPE environment who also faces sequence of returns risk from high portfolio withdrawals has double exposure to the valuation-return relationship. Having a somewhat more conservative allocation at retirement, or building a larger cash buffer, reduces the portfolio's exposure to a potential early-retirement valuation correction without requiring a complete exit from equities.
This question tests whether the plan's return assumption is calibrated to current conditions or uses a long-run average that may not reflect the current starting point.
This stress test applies a valuation-appropriate lower return scenario and reveals whether the plan has adequate resilience.
This question tests whether the advisor incorporates valuation awareness into portfolio positioning recommendations.
This is the sequence risk question applied to a specific valuation scenario. The answer should identify specific plan adjustments that would be made in response.
This question establishes whether the plan has been built with scenario sensitivity or only around a single return assumption.
The retirement planning calculator at plan.johnkoyle.com was built to model exactly the dynamics discussed in this paper. The retirement calculator at plan.johnkoyle.com uses Monte Carlo simulation that randomizes return sequences across 500 scenarios, automatically incorporating the possibility of poor early returns without requiring you to manually specify a CAPE-adjusted return assumption. The Monte Carlo approach captures the realistic range of outcomes including the scenarios where early returns are weak. To stress-test your specific concern about current valuations, try reducing the Gross Annual Return input by 1 to 2 percentage points from your base assumption and observe how the Monte Carlo success rate changes. This shows you directly how sensitive your plan is to a period of below-average returns in the critical early retirement years.
John Koyle, AIF®, is the Co-Founder of Red Cedar Wealth Advisors, headquartered in Pocatello, Idaho. He holds the Accredited Investment Fiduciary (AIF®) designation, awarded by the Center for Fiduciary Studies (Fi360), which signifies completed coursework, a rigorous examination, and ongoing continuing education in fiduciary responsibility and prudent investment practices.
John serves individuals and families in or approaching retirement throughout eastern Idaho, the Pacific Northwest, and across the country via Zoom. Clients work directly with John, not a junior team. Red Cedar Wealth Advisors operates under Osaic Wealth, Inc. (Member FINRA/SIPC) and Osaic Advisory Services, LLC for investment advisory services.
Every client relationship is built on five integrated disciplines. The proportions shift with the client and the moment. The integration is constant. Most of the actual value sits in how these disciplines connect, not in any single one of them.
Retirement planning is a discipline that barely existed a generation ago. For most of modern history, people worked until they physically couldn't and then they died, usually fairly close together. The idea that an individual should spend decades saving, then spend decades drawing down those savings, with a plan that accounts for inflation, taxation, sequence risk, healthcare, longevity, and estate transfer, that's maybe forty years old.
Which means almost nobody your age grew up watching their parents do it properly. There's no cultural muscle memory. The advice industry backfilled that gap with rules of thumb that work sometimes and fail catastrophically the rest of the time. The 4% rule. 'You can take Social Security at 62.' 'Target-date funds will handle it.' These are not bad starting points. They are terrible ending points. Real planning is specific, personal, and built on principles that hold up across the full range of outcomes, not just the average one.
The tax code is a set of instructions Congress wrote to shape behavior. Aligning your financial life with those instructions is not aggressive planning. It is the planning. Roth conversion sequencing, capital gains compression on concentrated positions, charitable remainder trusts, Social Security timing, beneficiary coordination. None of these are obscure. They're all legitimate, all written into the code intentionally, and all under-used. Most CPAs handle compliance. The strategy work is a different discipline entirely.
Seventy percent of family wealth doesn't survive two generations. The reason isn't bad markets. The cause is failure to communicate, outdated documents, and no plan for preparing heirs. Beneficiary designations regularly override well-crafted wills. Trust structures created a decade ago no longer match current law or current family. The portfolio that built the wealth isn't the structure that transfers it. The work here is coordinating with your attorney to align documents, beneficiaries, gifting strategies, and trust funding with what you actually want to happen.
Every week, before any portfolio decision, John runs through four layers of market health: economic conditions, market internals, valuations, and sentiment. Each layer gets scored and those scores combine into a composite that maps directly to a portfolio posture, from aggressive on the positive end to defensive on the negative. The work is in the scoring. Once the scoring is done, the positioning follows. That removes one of the most dangerous things in investing: making it up as you go.
The protection gap quietly kills more plans than markets do. A significant net worth paired with inadequate liability coverage is a lawsuit away from a serious problem. Long-term care is more acute: a multi-year care event for one spouse can consume what was meant for the survivor. Most advisors relegate risk to a footnote because insurance conversations are uncomfortable. The math doesn't care. Coverage adequacy, umbrella sizing, long-term care planning, and life insurance structure sit alongside the portfolio in any complete plan.
These are the principles behind every plan John builds.
To begin a conversation, visit johnkoyle.com, use the retirement planning calculator at plan.johnkoyle.com, or reach John directly at john@redcedarwealth.com or (208) 915-8400. Initial consultations are complimentary and carry no obligation.