Is the 4% Rule Still Valid? Updated Trinity Study Data

The Genesis of the 4% Rule

The genesis of the 4% rule can be traced back to a seminal 1998 study by three professors at Trinity University — Philip Cooley, Carl Hubbard, and Daniel Walz. This groundbreaking research, published in the AAII Journal as "Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable," rigorously tested various withdrawal rates against historical U.S. market data spanning 1926 through 1995, utilizing rolling 30-year periods.

Their key finding revealed that an initial 4% withdrawal rate, adjusted annually for inflation, achieved a remarkable 95% success rate over 30-year periods when applied to a balanced 50/50 stock/bond portfolio. This success rate climbed to 98% with a more aggressive 75/25 stock/bond allocation.

Notably, financial planner William Bengen independently arrived at similar conclusions in 1994. Publishing in the Journal of Financial Planning, Bengen identified what he termed the "SAFEMAX" — the maximum sustainable initial withdrawal rate — at approximately 4.15% for a 50/50 portfolio over 30-year periods, based on data from 1926 through 1992.

Together, these two influential studies solidified the 4% rule as the foundational benchmark in retirement income planning.

Updated Data Through Early 2024

Dr. Wade Pfau, a distinguished professor at the American College of Financial Services, has diligently maintained and updated these Trinity-style analyses. His most recent 2024 update, featured in the Retirement Researcher newsletter, extends the underlying dataset through December 2023 and largely reaffirms the rule's historical robustness:

• 4% withdrawal, 50/50 portfolio, 30 years: 96% historical success rate
• 4% withdrawal, 75/25 portfolio, 30 years: 98% historical success rate
• 4% withdrawal, 100% stocks, 30 years: 95% historical success rate

While raw historical data continues to support the 4% rule for traditional 30-year retirements, a closer examination reveals several critical factors that complicate its forward-looking applicability.

Test your own withdrawal strategy with the Retirement Withdrawal Calculator.

The Valuation Problem: Retiring into Expensive Markets

The historical success rates of the 4% rule are predicated on the assumption of retiring at a random point in market history. In reality, however, individuals commence retirement at a specific juncture, facing unique market valuations that significantly influence future returns.

As of early 2024, Robert Shiller's cyclically adjusted price-to-earnings ratio (CAPE) for the S&P 500 stood at approximately 34-35, significantly exceeding its historical median of about 16. Seminal research by Pfau (2013, "An International Perspective on Safe Withdrawal Rates") and Finke, Pfau, and Blanchett (2013, "The 4 Percent Rule Is Not Safe in a Low-Yield World," Journal of Financial Planning) has illuminated the profound impact of starting valuations:

• When the CAPE ratio exceeds 25 at the onset of retirement, the historically safe withdrawal rate drops to approximately 3.0-3.5%.
• Conversely, when the CAPE ratio is below 15, historical safe withdrawal rates have been as high as 5.5-6.0%.

Consequently, initiating retirement during periods of elevated valuations often translates to lower expected returns over the crucial initial decade – precisely when the detrimental effects of sequence-of-returns risk are most pronounced.

Sequence-of-Returns Risk: The Real Threat to Your Portfolio

The 4% rule's vulnerability extends beyond simply achieving adequate average returns; the order in which those returns occur, particularly in the critical first 5-10 years of retirement, is paramount.

To illustrate the profound impact of sequence-of-returns risk, consider two hypothetical retirees, each beginning with a $1 million portfolio and a 4% initial withdrawal rate:

• Retiree A experiences robust 10% annual returns for the first 10 years, followed by -5% annual returns for the next 5 years. After 15 years, their portfolio is worth approximately $1,180,000.
• Retiree B experiences detrimental -5% annual returns for the first 5 years, followed by strong 10% annual returns for the next 10 years. Despite the same average return over the 15-year period, their portfolio is worth approximately $680,000.

This staggering difference—approximately $500,000—is solely attributable to the sequence of returns. Early losses disproportionately compound against a shrinking portfolio already being depleted by withdrawals. As financial planning researcher Michael Kitces famously demonstrated (Nerd's Eye View blog, 2008), roughly 80% of a retiree's long-term outcome variance is explained by the real returns experienced in the first decade of retirement.

The Bond Yield Challenge

The original Trinity Study period (1926-1995) benefited from a significantly more favorable interest rate environment than recent decades. During that era, the 10-year Treasury yield averaged a robust 5.6%. In stark contrast, from 2010 through 2021, this average plummeted to approximately 2.1%.

Finke, Pfau, and Blanchett (2013) conducted Monte Carlo simulations incorporating forward-looking return assumptions derived from prevailing bond yields. Their research indicated that with 10-year Treasury yields at a mere 2%, the 4% rule's success rate for a 30-year retirement plummeted to approximately 50%.

While bond yields have recovered somewhat—with the 10-year Treasury hovering around 4.0-4.5% in early 2024 (U.S. Department of the Treasury Daily Yield Curve data)—this still remains below the long-term historical average that underpinned the original 4% rule's robust findings, though it significantly improves the outlook compared to the ultra-low yield environment of 2020-2021.

What About Longer Retirements?

The original Trinity Study was designed around 30-year retirement horizons, which is appropriate for someone retiring at 65 and living to 95. However, early retirees, perhaps commencing at age 50 or 55, face significantly longer horizons of 40-50 years or more.

Bengen's subsequent 2006 research specifically addressed longer retirement durations. He found that extending the retirement period from 30 to 40 years reduced the SAFEMAX from approximately 4.15% to about 3.5%. For even longer 50-year periods, the safe withdrawal rate dropped further to roughly 3.0%.

Karsten Jeske, a former quantitative analyst and author of EarlyRetirementNow.com, conducted an exhaustive 50-part Safe Withdrawal Rate Series (2016-2021) specifically tailored to early retirement scenarios. Utilizing an extended dataset from 1871 through 2023, Jeske's meticulous analysis revealed:

• 3.25% withdrawal, 75/25 stocks/bonds, 60 years: approximately 95% success rate
• 4.0% withdrawal, same portfolio, 60 years: approximately 75% success rate

Evidently, for those embarking on early retirement, the traditional 4% rule proves overly aggressive. A more conservative initial withdrawal rate of 3.0-3.5% offers a substantially greater margin of safety.

Check how your savings rate affects your target portfolio size with the Retirement Savings Calculator.

Flexible Withdrawal Strategies: Adapting to Market Realities

The inherent rigidity of the traditional 4% rule—mandating inflation-adjusted withdrawals irrespective of portfolio performance—is often impractical. In reality, few retirees adhere to such an inflexible approach. Recognizing this, several prominent researchers have proposed more dynamic and adaptive withdrawal strategies:

Guyton-Klinger Decision Rules

Jonathan Guyton and William Klinger (2006), in their seminal Journal of Financial Planning article, introduced a robust set of decision rules or "guardrails" designed to enhance sustainability:

• Skip the inflation adjustment in any year the portfolio declines.
• Cut withdrawals by 10% if the current withdrawal rate (withdrawal amount divided by current portfolio value) exceeds the initial rate by more than 20%.
• Increase withdrawals by 10% if the current rate falls below the initial rate by more than 20%.

By implementing these adaptive rules, the sustainable initial withdrawal rate for 40-year periods could be significantly increased to approximately 5.2-5.6%, representing a substantial improvement over a rigid 4% approach.

The Bucket Strategy

Pioneered by Harold Evensky (Evensky & Katz Wealth Management) and detailed in his 2006 book, Retirement Income Redesigned, the bucket strategy advocates for segmenting a portfolio. Typically, 1-2 years of living expenses are held in cash or short-term bonds (Bucket 1), with subsequent buckets allocated to longer-term growth assets. This approach strategically buffers against sequence-of-returns risk by ensuring that essential spending can be met without liquidating equities during market downturns.

Variable Percentage Withdrawal (VPW)

Developed by David Blanchett, Maciej Kowara, and Peng Chen of Morningstar (2012) in their paper "Optimal Withdrawal Strategy for Retirement Income Portfolios," the Variable Percentage Withdrawal (VPW) method dynamically adjusts the withdrawal amount each year. It calculates a new withdrawal percentage based on the current portfolio value and the retiree's remaining life expectancy. While this method virtually eliminates the risk of portfolio depletion by aligning spending with portfolio performance, it inherently means that spending levels can fluctuate and potentially decrease during adverse market conditions.

A Practical Framework for Today's Retiree

1. Start with 3.5-4.0% for a traditional 30-year retirement. Err on the side of caution, leaning towards 3.5% if market valuations (CAPE) are elevated (above 25) or bond yields remain below their historical averages.
2. Use 3.0-3.5% for early retirees facing 40+ year horizons.
3. Integrate flexibility: Implement adaptive strategies, such as Guyton-Klinger-style guardrails, which allow for reduced spending during market downturns and potential increases during periods of strong portfolio performance.
4. Establish a cash buffer: Holding 1-2 years of living expenses in highly liquid assets (cash or short-term bonds) significantly mitigates the risk of being forced to sell equities at depressed prices during market corrections.
5. Conduct periodic reassessments: Recognize that the "optimal" withdrawal rate is not static. Re-evaluate your strategy every 3-5 years, as your portfolio evolves, market conditions shift, and your remaining time horizon naturally shortens.

Frequently Asked Questions

What exactly is the 4% Rule?

The 4% rule dictates that in the first year of retirement, you withdraw 4% of your initial portfolio value. In subsequent years, this dollar amount is adjusted upwards for inflation, irrespective of your portfolio's performance. For example, with a $1 million portfolio, you would withdraw $40,000 in year one. If inflation is 2%, your year two withdrawal would be $40,800.

Has the 4% Rule Ever Failed Historically?

Yes, the 4% rule has historically failed in approximately 4-5% of 30-year periods. The most challenging starting years included 1929 and 1966, both characterized by high market valuations followed by prolonged periods of poor returns. Retirees who commenced their withdrawals in these years with a 4% rate and a 50/50 portfolio allocation would have depleted their funds before reaching the 30-year mark.

Should I Use a Lower Withdrawal Rate if I Retire Early?

Absolutely. For retirement horizons extending to 40 years, research consistently suggests a safer range of 3.0-3.5%. For even longer periods of 50-60 years, a rate of 3.0-3.25% is more appropriate. The extended duration significantly amplifies vulnerability to sequence-of-returns risk, necessitating a more conservative initial withdrawal rate.

Does Social Security Affect the 4% Rule Calculation?

Yes, Social Security significantly impacts your required portfolio size by reducing the amount you need to withdraw from your investments. For instance, if your annual spending is $60,000 and Social Security provides $24,000, you only need $36,000 from your portfolio. Using the 4% rule, this implies a required portfolio of $900,000 ($36,000 / 0.04) instead of $1.5 million ($60,000 / 0.04). Strategically delaying Social Security benefits to age 70 can further increase your guaranteed income, thereby reducing your reliance on portfolio withdrawals.

What Withdrawal Rate is Prudent in Today's Elevated Valuation Environment?

Given current market conditions, with the CAPE ratio often above 30-35, historical analysis suggests adopting a more conservative initial withdrawal rate of 3.0-3.5% for a traditional 30-year retirement. Crucially, this should be paired with flexible spending rules, such as Guyton-Klinger-style guardrails, to allow for potential increases if early retirement years prove favorable.