Try measuring something with a body part, and you’ll quickly see the problem with rules of thumb. Yet when it comes to money, many people still rely on them.
The phrase “rule of thumb” dates to the 1600s, when thumbs were used as makeshift rulers. It’s a fitting metaphor for how people sometimes treat retirement planning: Eyeballing major financial decisions with rough shortcuts that can wildly miss the mark.
One of the most well-known is the “120 minus your age” rule.
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According to this rule, you subtract your age from 120 to determine the percentage of your portfolio that should be in stocks, with the rest in bonds or other lower-risk assets. A 30-year-old might be 90% in stocks, while a 70-year-old would scale back to 50%.
Simple, right? But that’s also the problem.
As author Khaled Hosseini wrote, “Human behavior is messy and unpredictable and unconcerned with convenient symmetries.” Rules such as this treat everyone the same, when in reality, your emotions, habits and financial needs are just as important as your age.
That can be especially problematic for retirement. A T. Rowe Price survey found that people with a formal retirement plan — one that accounts for their income goals, investment strategy and tax considerations — felt far more confident about their future than those without one.
The '120 minus you rule' for retirement
Is there a better way to build your retirement portfolio?
Professionals say yes. It starts by factoring in not just your age, but you. Specifically, the parts of you that might lead to poor financial decisions, like emotional reactions, overconfidence and risk aversion.
Consider it the “120 minus you rule for retirement.”
Instead of subtracting only your age, you subtract the behaviors that could derail your plan, because while investor psychology mi be hard to measure, its impact is anything but.
Why the '120 minus your age rule' falls short
To understand why personalization matters, consider how generalizations often fall short when applied to your finances. The "120 minus your age rule," for instance, doesn’t account for current market conditions, your income needs or how you actually respond to risk.
“That kind of shortcut might’ve worked better in an era of predictable bond yields and linear career paths,” says Melissa Caro, CFP® and founder of My Retirement Network. “It doesn’t hold up as a standalone framework in today’s more complex environment.”
Nathan Sebesta, CFP® and founder of Access Wealth Strategies, adds: “While the 120 rule can be a decent starting point, it often oversimplifies the complex nature of investor behavior.” He recommends a portfolio based on both financial goals and, perhaps most important, emotional resilience.
Behavior matters. A lot.
JPMorganChase Institute research shows that investors tend to pour more money into the market after periods of strong performance — classic return-chasing behavior that can lead to buying high and selling low.
A 2013 academic paper (PDF) indicates that individual investors tend to underperform over time by trading too often, selling winners while holding losers and reacting to news cycles.
“Just because the target allocation is supposed to be a certain percentage doesn’t mean it behaviorally should be,” says Bill Shafransky, CFP® and financial adviser at Moneco Advisors.
He explains that even if the rule suggests an 80% stock allocation, that doesn’t mean you can, or should, stomach it. A 40-year-old might have the time horizon to justify an 80/20 portfolio, but if they panic during every market dip, a more balanced 60/40 mix might be the smarter choice.
What is the '120 minus you rule?'
Instead of defaulting to a formula, advisers encourage investors to tailor asset allocation based on real-life variables, the gist of the 120 minus you rule for retirement.
It blends the analytical with the behavioral. You start with fundamentals, such as historical returns, your time horizon and the level of return needed to support your goals. But you filter that through something most models ignore: You.
Consider that your comfort with market risk, such as a fingerprint, varies from person to person. It's shaped by experience, personality, even current events. Two people with the same age and income might have dramatically different reactions to volatility. One shrugs it off; the other loses sleep.
“If you can’t sleep at night when the market dips, even the best-designed plan won’t be effective,” Sebesta says.
Hence, financial advisers often use tools such as cash flow modeling, historical simulations and stress-testing to show what different allocations might feel like during real-world events. That insight can help you land on a strategy you’re not just told to stick with, but one you can.
The result? An allocation shaped not just by how the market works, but by how you do.
How to apply the '120 minus your age rule' to ... you
With the purpose of the 120 minus you rule in mind — to align your portfolio with both your goals and your gut — many advisers recommend a bucket strategy to help manage returns and reactions.
“Split your investments into different buckets using different allocations,” says Shafransky. “For example, one to two years’ worth of expenses might go into a conservative allocation, while the rest is invested more aggressively. That way, if the market drops, you know your near-term needs are covered, giving the rest of your money time to recover.”
This approach can help you avoid the dreaded sequence of returns risk.
On the behavioral side, risk-tolerance questionnaires can help establish a baseline. However, “risk tolerance isn’t static,” says Caro. “It can shift after a job loss, during caregiving, or simply with age and experience.”
She recommends revisiting your portfolio and any risk assessments regularly, not only to confirm they still reflect your comfort level, but to catch any disconnects before they lead to costly decisions.
This could mean having an in-depth conversation with your adviser, guided by questions such as: How did you respond during the market drops of 2008 or 2020? If your portfolio fell 25%, how would you feel? Would you stay the course or feel pressured to make changes?
As Sebesta puts it, the goal is to “find an allocation you can stick with — not just when times are good, but when the market tests your nerves.”
Put that way, the 120-you rule for retirement isn’t so much about improving how you invest, but rather, how you sleep at night.
More Retirement Rules
- The Rule of Retirement Inversion
- The Retirement Rule of $1 More
- The 'First Year of Retirement' Rule
- The Rule of 240 Paychecks in Retirement
- The 'Die With Zero' Rule of Retirement
- The '8-Year Rule of Social Security' — A Retirement Rule
- The Rule of 1,000 Hours in Retirement
- The 'Second Law' of Retirement Rules
- The Rule of Four Futures
- The Rule of $1,000: Is This Retirement Rule Right for You?
- The Rule of 55: One Way to Fund Early Retirement
- The 80% Rule of Retirement: Should This Rule be Retired?
- The 4% Rule for Retirement Withdrawals Gets a Closer Look
- The Rule of 25 for Retirement Planning: How Much Do You Need to Save?
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