The 100-Minus-Age Rule

Quick definition: The 100-Minus-Age Rule is a simple heuristic suggesting that your stock allocation percentage should equal 100 minus your age—so a 30-year-old holds 70% stocks, a 50-year-old holds 50% stocks, and a 70-year-old holds 30% stocks.

Key Takeaways

• The rule provides a memorable, easy-to-implement framework accessible to investors without financial planning expertise
• It aligns reasonably with modern target-date fund glide paths and academic asset allocation research
• The rule inherently assumes a time horizon extending to approximately age 95–100
• It remains applicable throughout life, automatically becoming more conservative as you age without requiring decisions
• While imperfect, the rule's simplicity often outweighs its limitations for beginning investors and those preferring passive management

The Rule's Simplicity and Appeal

The 100-Minus-Age Rule has endured for decades as a simple allocation framework precisely because it's easy to remember and implement. At any point in life, you can calculate your stock percentage in seconds: subtract your age from 100 and that's your stock allocation. Everything else goes to bonds and cash. A 35-year-old holds 65% stocks and 35% bonds. A 60-year-old holds 40% stocks and 60% bonds. The arithmetic requires no financial expertise.

This simplicity addresses a real problem in retail investing: decision paralysis. Many investors, particularly those without formal financial training, avoid developing an allocation strategy because they're uncertain of the right approach. The 100-Minus-Age Rule provides a low-friction starting point that's legitimately defensible. Rather than do nothing, an investor can immediately implement the rule and begin building wealth.

The rule also eliminates ongoing decision-making. Once implemented, the only action required is annually rebalancing back to the rule's indicated allocation as you age. If you're 45 and hold 55% stocks, you automatically shift toward 54% stocks at age 46, 53% at age 47, and so forth. This removes the burden of deciding whether to become more conservative—the rule handles it automatically.

Historical Origins and Evolution

The 100-Minus-Age Rule emerged from mid-twentieth-century financial planning literature, providing a simplified version of more sophisticated allocation frameworks. It gained widespread popularity through Vanguard founder John Bogle's writings and endorsements, establishing it as a core principle in indexing and passive investing education.

The rule's persistence reflects its pragmatic success. While modern target-date funds have made the rule less necessary—someone can simply select a target-date fund matching their expected retirement year—the rule remains valuable for those managing allocations independently. Its longevity indicates that the underlying principle of declining equity exposure with age is sound and has worked across multiple decades of market cycles.

Alignment with Target-Date Fund Glide Paths

The 100-Minus-Age Rule maps reasonably well onto modern target-date fund glide paths, though with important differences. A target-date 2050 fund (for someone perhaps 35 years old today) might target 80% stocks, while the 100-Minus-Age Rule suggests 65% stocks. The rule is moderately more conservative than many target-date funds, particularly in the early years.

At retirement (age 65), the rule suggests 35% stocks, while many target-date funds target 50% stocks. Here the rule is noticeably more conservative. This difference reflects the rule's inherent assumption: it assumes retirees will live to approximately 100 years old and will spend their portfolio throughout that period. It assumes continued spending into your 90s and early 100s, which requires gradual de-risking throughout retirement.

The convergence of the rule and modern target-date funds suggests both are capturing the same fundamental principle: appropriate risk declines with age because time horizons decline with age. The differences reflect nuanced assumptions about longevity, spending patterns, and the acceptable level of portfolio volatility.

Application Throughout Life Stages

The rule's value becomes apparent across different life stages. In early career (age 25), the rule suggests 75% stocks—an aggressive allocation appropriate for someone with 40 years to retirement. The high equity exposure captures the equity risk premium while allowing decades to recover from downturns.

In mid-career (age 40), the rule suggests 60% stocks—balanced growth allocation appropriate as retirement approaches and family responsibilities increase. The shift is gradual and doesn't require deciding whether to become more conservative; the rule automatically prescribes it.

At retirement (age 65), the rule suggests 35% stocks—conservative enough to provide portfolio stability during distribution years while maintaining meaningful equity exposure to hedge inflation across a potentially 30+ year retirement.

In advanced retirement (age 85), the rule suggests 15% stocks—heavily focused on income and capital preservation while acknowledging that someone at 85 with a 10–15 year life expectancy should hold minimal equity exposure. The gradual transition from 35% at age 65 to 15% at age 85 reflects ongoing sequence-of-returns risk mitigation.

Limitations and Drawbacks

Despite its elegance, the 100-Minus-Age Rule has limitations worth acknowledging. It assumes all investors have identical longevity expectations, risk tolerance, and financial situations. Someone with family history suggesting death at 80 would be over-invested in stocks according to the rule. Someone with strong longevity expectations or substantial non-portfolio income could comfortably hold more equities.

The rule also assumes you'll spend down your portfolio linearly, with continuing spending needs throughout your 90s. Someone planning to leave a substantial legacy to children or charitable causes might maintain higher equity allocations than the rule suggests. Someone planning to die with zero assets might accept more conservative allocations.

Additionally, the rule predates modern developments in target-date fund research. Current research on sequence-of-returns risk and the "through retirement" glide path philosophy suggests that continuing equity exposure through advanced age may be appropriate—meaning the rule might be overly conservative in later retirement.

The rule also doesn't account for non-portfolio wealth. Someone with substantial retirement income from pensions, Social Security, or ongoing employment can accept higher equity allocations than someone depending entirely on portfolio withdrawals. An individual with a $3 million portfolio and a $100,000 pension has fundamentally different risk tolerance than someone with a $500,000 portfolio and no pension income.

Variations and Modern Updates

The 100-Minus-Age Rule has spawned variations reflecting different assumptions. Some advisors suggest the "110-Minus-Age Rule" to account for increasing longevity and the research suggesting higher equity exposure throughout retirement can be appropriate. Others suggest adjusting the rule based on risk tolerance, using "95-Minus-Age" for conservative investors or "120-Minus-Age" for aggressive long-term investors.

These variations highlight that the rule is a framework, not a law. The specific number—100, 110, or 120—reflects assumptions about risk and longevity. For someone investing today, with likely life expectancy extending into their 90s or beyond, 110-Minus-Age might be more appropriate than 100-Minus-Age.

Practical Implementation

For investors choosing to use the 100-Minus-Age Rule, implementation is straightforward. Calculate your target stock percentage, select a diversified index portfolio (either a target-date fund or a three-fund portfolio), rebalance annually to return to the rule's indicated allocation, and then let compounding work.

The annual rebalancing required by the rule's shift—moving from 65% stocks to 64% stocks as you age from 35 to 36—is minimal. Most investors won't notice this shift in their portfolio holdings. However, it provides the psychological and mathematical benefits of gradually de-risking throughout life.

For those uncomfortable with manual rebalancing, a target-date fund provides automatic implementation of a similar principle without needing to remember the rule or perform annual calculations.

Next

Explore the 110-Minus-Age Rule, a modern update to the classic heuristic that reflects current longevity research and contemporary portfolio theory.