I spent 45 years as a CPA, 10 as a Wall Street investment advisor, and was awarded two Emmys as a financial journalist.
Here’s what I’ve learned about the mistakes that quietly cost retirees the most money.
These mistakes don’t show up in your quarterly statement. They compound in the background — in your tax bill, your withdrawal sequence, your Social Security decisions, your cash position.
By the time most people spot them, the window to fix them has closed. Here’s how to catch them before it does.
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Mistake #1: Not Knowing Your Real Retirement Number
Most people guess. They pick a round figure — $500,000, $1 million — and assume it’ll be enough.
But your actual retirement number depends on variables most people never calculate: your expected Social Security benefit, your healthcare costs in retirement (which are climbing faster than general inflation), your state’s tax treatment of retirement income, your expected lifespan, and your withdrawal rate.
Get any one of these wrong, and you can come up tens of thousands of dollars short over a 25-year retirement. Get two wrong, and you might outlive your money entirely.
The fix: Run a real projection — not a back-of-the-envelope estimate. Most people find their actual number is 15% to 30% different from what they assumed. That difference almost always matters.
Mistake #2: Ignoring the Tax Bomb in Your 401(k)
Here’s something your quarterly statement doesn’t show you: a significant portion of your traditional 401(k) isn’t yours.
The IRS gets their cut the moment withdrawals start. For most households near retirement, that bill runs $50,000 to $100,000 more than it needs to — not because the tax is avoidable entirely, but because the timing and sequencing of withdrawals is almost never optimized.
Those withdrawals can push you into higher tax brackets, trigger higher Medicare premiums, and increase the part of your Social Security that gets taxed.
A retiree who doesn’t plan withdrawals strategically can easily give up an extra $50,000 to $100,000 in unnecessary taxes over retirement.
Roth conversions, tax-loss harvesting, and coordinated withdrawal sequencing can dramatically reduce this bill — but only if you plan for them in the years before you retire. Once you’re already drawing down, most of the best options are off the table.
The fix: Map your withdrawal order before you retire, not after. This is one of the highest-leverage things a fiduciary does in the first meeting.
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Mistake #3: Claiming Social Security at the Wrong Time
For a married couple with average earnings histories, the difference between both spouses claiming at 62 versus optimizing the timing can exceed $150,000 in lifetime income. Most couples spend more time picking a refrigerator.
And yet most people claim early — often because they didn’t realize how much they were leaving on the table, or didn’t coordinate the decision with their spouse’s earnings history and survivor benefits.
There’s no universally right age. For some people, 62 really is the best answer. For others, waiting until 70 adds six figures to their lifetime income. It depends on your health, your spouse’s earnings record, your other income sources, and your tax situation.
What almost everyone gets wrong is making this decision alone, without running the actual numbers.
The fix: Model the claiming decision — both spouses, multiple scenarios — before you file. Once you claim, you can’t undo it.
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Mistake #4: Leaving Too Much Money in Cash “To Be Safe”
This is the most counter-intuitive mistake on this list, and the one that catches the most careful savers.
After a lifetime of building wealth, moving everything to cash or CDs as retirement approaches feels responsible.
It feels safe. It isn’t.
Inflation doesn’t stop when you retire. A $500,000 cash position loses roughly $15,000 to $20,000 in real purchasing power every year at recent inflation rates.
Over a 20-year retirement, that’s $300,000 to $400,000 in lost buying power — not from a market crash, not from a bad decision, just from sitting still.
The right allocation depends on your specific situation, your other income sources, and your risk tolerance. But an all-cash position is almost never the right answer, regardless of how safe it feels.
The fix: Think about cash as covering your near-term expenses — 1 to 2 years — and keep the rest invested appropriately for your timeline.
Mistake #5: Trying to Go It Alone
All four mistakes above have one thing in common: a good fiduciary catches them in the first meeting. Without one, they’re almost always missed.
This isn’t a knock on people who manage their own money. Plenty of people do it successfully during their working years, when the math is simple: save, invest, repeat.
Retirement planning is a different discipline. It involves tax optimization, Social Security timing, Medicare decisions, withdrawal sequencing, estate planning, and risk management — all at once, all interacting with each other, with no room for do-overs.
As a CPA and former Wall Street advisor, I’ve seen this firsthand: the people who navigate retirement well almost always have a qualified second opinion on their plan.
The research backs this up. Vanguard’s Advisor’s Alpha study estimates that working with a qualified advisor adds roughly 3% per year in net returns for retirees — primarily through better tax decisions and behavioral coaching during market downturns. On a $500,000 portfolio, that’s $15,000 a year. Far more than most advisors charge.
The catch: not all advisors are equal. A fiduciary is legally required to act in your interest — not earn commissions from the products they recommend. And finding a good one used to be hard.
That’s changed.
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Advisors in the network are legally required to act in your interest, not sell you products for commissions — and nearly all offer a free first appointment.
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The Bottom Line
The math on retirement mistakes is unforgiving.
A 3% advisor optimization on a $500,000 portfolio is $15,000 a year. A wrong Social Security decision can cost $150,000 over a lifetime. A poorly sequenced 401(k) withdrawal can add $50,000 to $100,000 in unnecessary taxes. These aren’t small numbers — and none of them announce themselves.
The people who avoid them tend to have one thing in common: they sat down with a fiduciary before the window closed.
If anything in this article sounded familiar, that meeting is worth having. The matching questionnaire takes about 10 minutes and the service is completely free. The cost of skipping it isn’t.
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Stacy Johnson is the founder of MoneyTalksNews.com, a CPA since 1981, a former investment advisor at major Wall Street firms, and a two-time Emmy Award winner for personal finance journalism.
MoneyTalksNews is an independent personal finance publisher. We may earn a referral fee from partner services at no cost to you. Our editorial recommendations are based on merit, not compensation.
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