The 4% rule does not preserve capital. It was designed to deplete a portfolio over a 30-year retirement without running out early, and in many historical scenarios it did exactly that, ending near zero rather than near the starting balance. Whether the 4% rule preserves capital or spends it down comes down to a distinction most retirees never draw clearly: portfolio longevity and capital preservation are two different goals, and the rule solves for the first, not the second.
Longevity means your money outlasts you, even if only a few hundred dollars remain at the end. Preservation means the original principal stays intact, so you could hand the same starting balance to an heir or keep drawing from it past year 30. The rule considers it a complete success if the account hits zero on the last day of the 30th year. For a retiree hoping to leave an inheritance or fund a longer-than-expected life, that outcome is a failure.
What the Rule Was Actually Built to Do
Financial advisor William Bengen introduced the concept in a 1994 study published in the Journal of Financial Planning. He tested historical U.S. market data going back to 1926, looking for a withdrawal rate that could survive the worst economic stretches in American history, including the Great Depression and the stagflation of the 1970s. His target was simple: find a rate that kept a portfolio alive for exactly 30 years, even for a retiree unlucky enough to start during a major downturn.
Bengen’s research assumed a portfolio split evenly between stocks and intermediate-term government bonds, and he concluded that stock allocations below 50 percent or above 75 percent were counterproductive for sustaining withdrawals.1Financial Planning Association. The 4 Percent Rule Is Not Safe in a Low-Yield World Using a 50/50 portfolio, the 4 percent rate succeeded in 100 percent of historical rolling 30-year periods when paired with intermediate-term government bonds.2Financial Planning Association. Sustainable Retirement Spending With Low Interest Rates: Updating the Trinity Study The 30-year window was chosen because it roughly matches the life expectancy of someone retiring in their mid-60s. The whole exercise was about not running out of money, not about keeping the original balance intact.
Bengen himself later revisited his numbers and increased his recommended starting withdrawal rate to 4.7 percent, reflecting additional asset classes and updated data. That revision reinforces his original mindset: the goal was always the maximum safe spending rate, pushing the portfolio as hard as it could go without failing before the end of the term.
Why the Mechanics Deplete Principal
A true preservation strategy limits spending to the income a portfolio generates, typically dividends and interest, without touching the underlying assets. The 4% rule works differently. Following it on a $1,000,000 portfolio means taking $40,000 in year one and adjusting upward for inflation every year after that, regardless of what the market does. In many historical periods, that pace of spending consumed a meaningful chunk of the starting balance by year 15 or 20, even though the portfolio ultimately survived to year 30.
The inflation adjustment is the mechanism that drives depletion. You increase your withdrawal amount based on the Consumer Price Index for All Urban Consumers, maintained by the Bureau of Labor Statistics, not on how your portfolio performed.3U.S. Bureau of Labor Statistics. Consumer Price Indexes Overview Withdraw $40,000 in year one with 3 percent inflation, and you take $41,200 in year two whether the portfolio gained or lost value.
That mechanical adjustment protects purchasing power, but it can far exceed 4 percent of the current balance during rough stretches. If a portfolio drops 15 percent in a bad market year while inflation pushes the withdrawal amount up 5 percent, the retiree is pulling a much larger share from a smaller pool. That combination accelerates principal consumption in a way compound growth may never fully undo. Bengen’s model survived the double-digit inflation of the late 1970s only because strong subsequent stock returns eventually compensated. Retirees living through those years watched their annual withdrawal amounts balloon well above 4 percent of what remained, and their portfolios shrank significantly before recovering.
Sequence of Returns Decides the Outcome
The order in which you experience market returns matters more than the average return over 30 years. Two retirees can have identical average annual returns and end up with wildly different balances depending on when the bad years hit. A steep decline in years one through three forces a retiree to sell more shares at depressed prices to meet the withdrawal target. Those shares are permanently gone and cannot participate in any recovery that follows.
This is what separates the best-case from the worst-case outcomes under the rule. A retiree who starts during a strong bull market builds a cushion that absorbs later downturns. A retiree who starts during a crash locks in losses while simultaneously drawing capital, creating a hole the portfolio may never climb out of. In Bengen’s historical testing, the worst starting years were those immediately preceding or during major bear markets, and those retirees came closest to exhausting their accounts by year 30.
One common defense against sequence risk is a cash reserve outside the investment portfolio, drawn on during downturns instead of selling depreciated assets. Research on bucket strategies found that setting aside one year of withdrawals in cash outperformed setting aside two, three, or five years, with a failure rate as low as 1.2 percent when paired with certain rebalancing rules.4IESE Business School. The Bucket Approach for Retirement: A Suboptimal Behavioral Trick? Holding five years in cash actually made things worse, pushing failure rates above 25 percent, because so much of the portfolio sat in a non-growing asset that long-term returns suffered.
Forces That Speed Depletion Beyond Your Control
Even a retiree who wants to underspend the 4% rule to protect principal runs into rules and costs that push withdrawals higher than planned.
Required Minimum Distributions
Qualified retirement plans, traditional IRAs, and 403(b) accounts are all subject to required minimum distribution rules.5eCFR. 26 CFR 1.401(a)(9)-1 – Minimum Distribution Requirement in General Under SECURE 2.0, distributions must begin at age 73 for anyone born between 1951 and 1959, and at age 75 for anyone born in 1960 or later.
The RMD calculation divides your account balance by a life expectancy factor that shrinks each year. By your early 80s, the required percentage can exceed 5 or 6 percent of the balance, well above the 4 percent target. When that happens, you deplete capital faster than planned, and the tax bill grows with it. Missing an RMD entirely triggers an excise tax of 25 percent of the shortfall, reduced to 10 percent if corrected within the IRS window.6Office of the Law Revision Counsel. 26 USC 4974 – Excise Tax on Certain Accumulations in Qualified Retirement Plans Roth IRAs are the exception. They carry no RMDs during the original owner’s lifetime, which makes them a useful vehicle when preservation is a priority.
Tax Drag
The 4% rule calculates gross withdrawals, not what lands in your checking account. Every dollar pulled from a traditional 401(k) or IRA is taxed as ordinary income. Once Social Security, pension payments, and investment income get added on, retirees often move into the 22 or 24 percent bracket faster than they expect. Larger withdrawals can also trigger income-related monthly adjustment amounts on Medicare Part B and Part D premiums, which can more than triple the standard premium at the highest income tiers.7Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles Medicare uses a two-year lookback, so a single spike year, such as a Roth conversion, raises premiums two years later.
Withdrawals also affect how much Social Security gets taxed. Once combined income exceeds $34,000 for a single filer or $44,000 for a married couple, up to 85 percent of benefits become taxable. Those thresholds have not been indexed for inflation since 1993. Starting in 2026, the One, Big, Beautiful Bill Act adds a new above-the-line deduction of up to $10,000 for seniors receiving Social Security income, phasing out for single filers above $100,000 in modified adjusted gross income and joint filers above $200,000.8Internal Revenue Service. One, Big, Beautiful Bill Act: Tax Deductions for Working Americans and Seniors The practical effect: a 4 percent gross withdrawal may deliver only 3 percent or less in actual spending power once federal taxes, Medicare surcharges, and Social Security taxation interact.
The Early Withdrawal Penalty
The rule assumes a traditional retirement age. Retiring earlier introduces another cost: withdrawals from qualified plans and IRAs before age 59½ generally face a 10 percent additional tax on top of regular income tax.9Office of the Law Revision Counsel. 26 USC 72 – Annuities; Certain Proceeds of Endowment and Life Insurance Contracts Exceptions exist, including substantially equal periodic payments under Section 72(t) and separation from service during or after the year you turn 55 for employer plans.10Internal Revenue Service. Retirement Topics – Exceptions to Tax on Early Distributions For early retirees who use the 4% rule without qualifying for an exception, the penalty adds a drag the original model never accounted for.
What Rate Actually Preserves Capital
If the goal is to spend from a portfolio for 30 years and end with roughly the same inflation-adjusted balance, the historically safe rate drops well below 4 percent. Most research puts it in the range of 2 to 3 percent, depending on asset allocation and which historical period you stress-test against. At those rates, you are much more likely to spend only the real returns above inflation and leave the principal intact.
On a $1,000,000 portfolio, that is the difference between $40,000 a year and $20,000 to $30,000 a year. For many retirees, that gap is the difference between a comfortable lifestyle and a tight one, which is exactly why Bengen’s original work targeted the highest sustainable rate rather than the preservation rate. He was solving for the retiree who needed maximum income, not one trying to build a legacy.
Dynamic Alternatives That Lean Toward Preservation
The biggest weakness of the 4% rule for a preservation-minded retiree is its rigidity: set a dollar amount in year one, ratchet it up for inflation, and ignore what the portfolio does. Several alternatives tie withdrawals to actual portfolio performance, which naturally protects capital during downturns.
The Guyton-Klinger guardrails method sets upper and lower boundaries around the initial withdrawal rate. If the current-year withdrawal rate drifts more than 20 percent above the starting rate, meaning the portfolio has dropped significantly, the retiree cuts that year’s withdrawal by 10 percent. If the rate falls more than 20 percent below the starting rate, the retiree takes a 10 percent raise.11Financial Planning Association. Decision Rules and Maximum Initial Withdrawal Rates The tradeoff is income volatility.
The variable percentage withdrawal method recalculates spending each year based on current balance, an expected rate of return, and remaining life expectancy.12Financial Planning Association. Making Sense Out of Variable Spending Strategies for Retirees When markets drop, the calculated withdrawal drops with them, automatically protecting principal. When markets rise, spending rises. This approach virtually eliminates the risk of total exhaustion, but it requires tolerance for years where income might decline 15 or 20 percent.
Both methods share a philosophy: to make the portfolio survive longer or end with a meaningful balance, a retiree has to accept less predictable income. The 4% rule chose predictability over preservation. Dynamic strategies reverse that choice.
The realistic middle ground for most retirees sits between the fixed 4 percent approach and strict preservation. Using a dynamic strategy, keeping a modest cash buffer, running Roth conversions before RMDs start, and cutting spending after bad market years can collectively push the ending balance much higher than the pure 4 percent model predicts. None of those adjustments guarantee preservation, but they shift the odds meaningfully in that direction.