The Rule of 100 for retirement investing is a quick formula for splitting your savings between stocks and bonds: subtract your age from 100, and the result is the percentage to keep in stocks. A 30-year-old lands at 70% stocks and 30% bonds. A 60-year-old flips closer to 40% stocks and 60% bonds. The formula is deliberately simple, and that simplicity is both its strength and its biggest blind spot.
How to Run the Math
Start with 100. Subtract your current age. That number is the share of your investment portfolio that goes into stocks. Everything left over goes into bonds or other fixed-income investments.
- A 35-year-old: 65% stocks, 35% bonds.
- A 50-year-old: 50/50.
- A 70-year-old: 30% stocks, 70% bonds.
Your stock allocation shrinks by one percentage point every year you age. No spreadsheet, no advisor, no math beyond grade-school subtraction. That’s the appeal. Someone with no investing background gets a defensible starting point that adjusts over a lifetime.
Why the Stock Share Shrinks With Age
Stocks deliver higher long-term returns than bonds, but they come with sharper drops along the way. A 35% market decline is painful at any age. The consequences are not. A 30-year-old with decades of paychecks ahead can wait for the recovery. A 67-year-old pulling money out for groceries and rent cannot, and may be forced to sell at the worst possible time.
Planners sometimes describe this as a shift from human capital to financial capital. Early in your career your biggest asset is not your investment account; it’s your future earning power. That stream of future paychecks acts like a giant bond, delivering stable income regardless of what the market is doing. As you approach retirement that earnings stream dries up, and your portfolio has to carry the full weight. The Rule of 100 mirrors that transition by gradually tilting your investments toward stability.
Why Many Planners Now Use 110 or 120
The original rule was built when Americans retired earlier and did not live as long afterward. Today’s numbers look different. According to the Social Security Administration’s most recent period life table, a 65-year-old man can expect to live roughly another 17.5 years, and a 65-year-old woman about 20 more years. 1Social Security Administration. Actuarial Life Table A retirement portfolio may need to last into the mid-80s or beyond, and a 35% stock allocation at age 65 might not generate enough growth to keep pace with inflation over two decades.
That is why much of the planning world has moved toward 110 or 120 as the starting number. Using 110, a 65-year-old would hold 45% stocks instead of 35%. Using 120, the same person targets 55% stocks. The higher starting number keeps more money working in growth investments during a retirement that could stretch 25 or 30 years. Which version fits depends on how comfortable you are riding out market swings and how much guaranteed income you’ll have from Social Security or a pension.
What the Rule Doesn’t Account For
Any formula that reduces your financial life to a single subtraction problem is going to miss things. The Rule of 100 ignores several factors that matter a lot in practice.
Risk tolerance. Some people sleep fine through a 30% market drop. Others panic-sell and lock in losses. Your emotional relationship with volatility often matters more than your age. A 40-year-old who cannot stomach watching their balance fall should probably hold more bonds than the rule suggests, whatever the math says.
Other income sources. If you’ll receive a solid pension or substantial Social Security benefits, those payments function like bond income you already own. Your investment portfolio can afford to lean more heavily toward stocks, because your living expenses are partly covered no matter what the market does. Two 65-year-olds with identical portfolios may reasonably end up with very different stock allocations if one has a generous pension and the other has none.
Spending needs relative to assets. Someone with $3 million saved who spends $60,000 a year is in a different position from someone with $500,000 who spends the same amount. The first person can afford to be aggressive because the portfolio vastly exceeds the need. The second needs to be more careful. The rule treats both identically.
Debt and near-term goals. If you’re carrying high-interest debt or saving for a house you plan to buy in three years, your asset allocation involves more than your retirement horizon.
Treat the rule as a default setting you adjust based on your actual circumstances, not a mandate.
Target-Date Funds: The Rule on Autopilot
If the Rule of 100 appeals to you but you’d rather not manage the allocation yourself, target-date funds do roughly the same thing automatically. You pick a fund named for the year you plan to retire, and the fund manager gradually shifts the stock-to-bond ratio over time along a predetermined “glide path.” Nearly 98% of 401(k) plans now use target-date funds as the default investment for employees who don’t make an active choice. 2Fiducient Advisors. The Evolution of Qualified Default Investment Alternatives If you’ve never touched your 401(k) elections, there’s a good chance your money already sits in one.
The glide paths used by major fund companies don’t follow the Rule of 100 exactly. Vanguard’s Target Retirement 2030 Fund, built for someone retiring around 2030, held roughly 59% stocks and 40% bonds as of March 2026. 3Vanguard. Vanguard Target Retirement 2030 Fund Under the classic Rule of 100, a person retiring in 2030 at age 60 to 65 would hold only 35% to 40% stocks. Vanguard keeps the mix more aggressive, reflecting the same longevity reasoning behind the Rule of 110 or 120.
One thing worth knowing: target-date funds don’t stop adjusting at retirement. Vanguard’s glide path, for example, continues shifting the mix well into the investor’s 70s. 4Vanguard. Target-Date Fund Glide Path The fund does not dump everything into bonds the moment you turn 65, because you’ll still need some growth to sustain withdrawals over a long retirement.
Sequence of Returns Risk Near Retirement
The years right before and right after you retire are when the Rule of 100 matters most, because of a concept called sequence of returns risk. Two retirees can earn the same average return over a five-year span, but if one of them gets the bad years first, the damage compounds in a way that’s very hard to reverse. One illustration showed two retirees with identical $1 million portfolios and $60,000 annual withdrawals, both averaging 6% returns over five years. The one who drew bad returns early ended up with more than $83,000 less than the other, purely because of the order the returns arrived in.
This is where the Rule of 100 earns its keep: it pushes you toward a more conservative mix precisely during the window when sequence risk is highest. The rule alone isn’t enough, though. Most planners also recommend keeping roughly two years of living expenses in cash or cash equivalents, outside your investment portfolio entirely. That cash buffer lets you cover expenses during a downturn without selling stocks at depressed prices.
Does ERISA Require You to Use the Rule of 100?
No. You’ll sometimes see the Rule of 100 discussed alongside ERISA, the federal law governing employer-sponsored retirement plans, so it’s worth drawing the line clearly. ERISA sets minimum standards for plan administration: how plans disclose information to participants, how quickly benefits vest, and what fiduciary duties plan managers owe to employees. 5U.S. Department of Labor. Employee Retirement Income Security Act (ERISA) It does not tell your employer or plan manager which asset allocation to use, and it does not endorse the Rule of 100 or any other allocation formula. The Department of Labor has maintained an “asset-class neutral position,” leaving specific investment decisions to plan fiduciaries exercising their own judgment. 6Federal Register. Fiduciary Duties in Selecting Designated Investment Alternatives
Your 401(k) plan offers a menu of investment options, but nobody is legally required to structure that menu around the Rule of 100. The allocation decision is yours.