21 DIY Investing Mistakes That Can Cost You More Than Fees

Phil Weiss, CFA®, CPA

13 hours ago

(And why it often shows up first as uncertainty.)

If you manage your own investments, you already know the obvious tradeoff. You save on advisor fees.

But there’s another cost that’s easy to miss. Many DIY investing mistakes do not look like mistakes at first. They look like reasonable decisions made without the full picture. It’s not a line item on a statement. It’s the uncertainty tax. You pay it in extra decisions, extra worry, and the nagging sense that you might be missing something.

Near retirement or after a major life change, uncertainty can get expensive fast. Not because you picked the wrong investment. More often, it happens because one decision triggers five others: Taxes, Medicare surcharges, withdrawal order, risk level, and timing start colliding.

While we’re working, most investing decisions revolve around saving and accumulating. Retirement shifts the focus to withdrawing money, managing taxes, protecting cash flow, and avoiding costly timing mistakes. A lack of familiarity with these new rules can make it easy to miss issues that cost money.

At first, DIY investing may feel like choosing funds and keeping costs low. Over time, especially near retirement, it often becomes DIY tax planning, DIY withdrawal planning, and DIY risk management too.

Two quick examples

Example 1. Approaching retirement

You’re 12 to 24 months from retiring. The market is volatile. You keep asking, “Should I de-risk my portfolio now?” You make a change, then worry you did it at the wrong time. Then you change it again.

You’re not making one decision. You’re making the same decision repeatedly, with increasing stress.

Example 2. Newly divorced or widowed

You now have to make decisions on your own. You want to simplify. You also don’t want to make a mistake. You consider “cleaning up” your taxable account by reducing the number of holdings, then realize it could trigger capital gains. The investment decision becomes a tax decision. Now you’re stuck.

That’s the pattern. DIY investing mistakes often start with uncertainty. Then they appear as tax surprises or retirement timing issues.

The issue is not that DIY investors are careless. The issue is that the closer you get to retirement, the more one decision affects several others.

Here are 21 DIY investing mistakes that may be costing you more than fees. I’m not listing these to shame anyone. I’m listing them because most people don’t notice the pattern until it creates a tax surprise, timing problem, or confidence problem.

You do not need to read this as a scorecard. Scan the list and notice which items create the strongest reaction.

Decision and process

1. You second-guess decisions after you make them.

Example: You make a change to your portfolio or your budget, then spend a week consuming opposing opinions to see if you messed up.

Cost: You lose momentum and avoid, or at least delay, the next decision.

Do this instead: Before you act, write down why you’re acting in one sentence.

2. You change course based on headlines or market noise.

Example: “Recession” leads to going to cash. “Rising rates” lead to dumping bonds.

Cost: You end up trading based on your anxiety.

Do this instead: Set a rebalancing rule and follow it, even when it feels boring.

3. You can’t explain why you own each holding.

Example: You own multiple investments that all sound diversified, but you can’t describe what each one does.

Cost: When markets drop, or you need to raise some cash, you don’t know what to keep, what to trim, or what to ignore.

Do this instead: Give every holding a job: Growth, income, stability, inflation protection, or diversification.

4. You don’t have written rules for buying, selling, and rebalancing.

Example: You rebalance when you feel uneasy, not when allocations drift. You don’t have a process you can consistently follow. Instead, you rely on guesswork.

Cost: Inconsistency creates avoidable mistakes.

Do this instead: Pick one rule. Annual, or when allocations drift by a set percentage.

5. You keep cash on the sidelines waiting for clarity.

Example: Cash builds up because “I’ll invest when things settle down.”

Cost: Clarity rarely arrives on schedule. Cash becomes a strategy by accident. Holding too much cash can also compromise returns and cause your portfolio to lag inflation, weakening your

Do this instead: Decide what cash is for: emergencies, near-term spending, or a planned portfolio allocation.

Portfolio design and risk

6. You own overlapping funds and don’t realize it.

Example: You own an S&P 500 index fund, plus a total market fund, and a large-cap growth fund.

Cost: You think you diversified, but you actually duplicated exposure, leaving more of your portfolio allocated to one segment of the market than you intended.

Do this instead: Map overlap once a year. If two funds do the same job, keep one.

7. One stock, sector, or theme is a large part of your portfolio.

Example: Employer stock, tech concentration, or one “AI” idea.

Cost: Your future becomes tied to one storyline.

Do this instead: Cap single positions. If taxes make selling hard, reduce the concentration over time with a plan.

8. You base your risk level on a feeling rather than a written plan.

Example: You say, “I’m conservative,” but you’re 90% stocks, or you panic at a 10% market drop.

Cost: You discover your true risk tolerance in the worst moment.

Do this instead: Define risk in real terms. “What drawdown can I hold without changing course?”

9. You haven’t stress-tested a 20-30% drop against your timeline.

Example: You assume you’ll ride it out, but retirement is close, and withdrawals are coming.

Cost: Normal market behavior can lead to poor timing decisions.

Do this instead: Run one scenario. If the market drops 25%, what changes, if anything? Does your plan still support your spending needs, or should you reduce risk before retirement withdrawals begin?

10. You don’t have 12 to 24 months of spending in safer assets.

Example: You’re retired and fully invested, so you need to take regular withdrawals regardless of the market’s movements.

Cost: You may sell at a low price to fund your daily needs.

Do this instead: Keep a cash or short-term bond allocation sized to your needs. For many retirees, that might mean setting aside enough to cover 18 to 24 months of planned withdrawals.

This strategy lets you draw from cash during a market downturn and can help reduce the need to sell investments at depressed prices. At Apprise, we often use this type of structure to create a buffer between short-term market volatility and spending needs.

Some of the most expensive DIY investing mistakes show up when investing decisions create tax consequences you did not expect.

Taxes and account choices

11. You sell in taxable accounts without checking the tax impact first.

Example: You “clean things up” to simplify your portfolio and trigger large capital gains.

Cost: You may pay taxes sooner than necessary, or in a higher bracket than necessary.

Do this instead: Before you sell, check the gain, the holding period, and how it stacks up with other income.

12. You’ve been surprised by capital gains or a higher bracket.

Example 1: You sell positions in the same year as a bonus, severance, home sale, or Roth conversion.

Example 2: You hold mutual fund positions in your taxable account. A fund realizes gains and distributes them to shareholders, sometimes late in the year, even if you did not sell your shares.

Cost 1: Income stacking can push you into higher rates now and higher Medicare premiums later.

Cost 2: You owe unexpected capital gains taxes, which could also contribute to underpayment penalties.

Do this instead: Run a rough projection before year-end. Even an estimate can reduce the chance of a surprise.

13. You harvest capital losses, but you’re not confident about the wash-sale rules.

Example: You sell at a loss, but an automated investment plan repurchases the same or a substantially identical security within the 61-day wash sale window in another account. (The wash-sale window starts 30 days before you sell the security and lasts until 30 days after you sell it.) Note that this rule applies even if you sell in your taxable account and repurchase in an IRA or a Roth IRA.

Cost: The loss may be disallowed or deferred when you expected to use it.

Do this instead: Pause automatic buys and coordinate across accounts for 31 days.

14. You give cash to charity when appreciated securities or a QCD may be better options.

Example 1: You want to make a charitable donation, so you sell a stock with a large gain and donate the cash. Alternatively, you write checks while sitting on highly appreciated taxable investments.

Cost: You may pay capital gains tax when you could have avoided it.

Do this instead: When the rules apply, donating appreciated securities directly to charity may allow you to avoid tax on the unrealized gain and, if you itemize, potentially deduct the fair market value.

Example 2: You are age 70½ or older. You take a distribution from your IRA and donate the cash.

Cost: You pay ordinary income tax on the distribution and, depending on your tax situation, you may or may not qualify for a tax deduction.

Do this instead: Make a qualified charitable distribution (QCD) directly from your IRA to the charity. When you follow the applicable rules, the QCD can count toward satisfying your required minimum distribution (RMD), and you also generally exclude a qualifying QCD from taxable income.

Overall guidance. Review giving once a year. Decide if appreciated assets, donor-advised funds, or QCDs apply. (See also our recent blog on tax-efficient charitable giving.)

15. You choose investments without thinking about asset location.

Example: High-yield bonds in taxable accounts and tax-efficient stock funds in IRAs. Or holding your highest-expected-growth assets in tax-deferred accounts when holding them in a Roth or HSA may better support the plan.

Cost: Potentially higher taxes without improving the portfolio.

Do this instead: Place tax-inefficient investments in retirement accounts when appropriate. Hold tax-efficient broad equity funds in taxable accounts when appropriate, and consider using Roth accounts for assets with higher expected growth. (See this blog for more about asset location.)

Retirement and distribution planning

16. You don’t have a coordinated withdrawal plan for taxable, IRA, HSA, and Roth accounts.

Example: You withdraw from the IRA because “that’s retirement money,” while taxable, Roth, and Health Savings Account (HSA) assets sit untouched.

You fail to consider your long-term plan when withdrawing funds. The goal should be to minimize the taxes you pay over your lifetime, not to have a very low tax bill in a particular year.

Cost: Different account types are taxed differently. Failing to consider your marginal tax bracket both now and in the future can result in paying more in taxes over your lifetime. Your withdrawal mix can reduce or increase your lifetime tax bill.

Do this instead: Establish a plan that looks at the big picture, then pressure-test it against your tax bracket, cash-flow needs, and goals.

17. You haven’t reviewed Medicare surcharges (IRMAA) and MAGI timing.

Example: A Roth conversion or big gain triggers higher Medicare premiums two years later.

Cost: You pay higher Medicare premiums without realizing why.

Do this instead: Check the current Income-Related Monthly Adjustment Amount (IRMAA) brackets before large income events, especially in the years before and after Medicare begins.

Be aware that the IRMAA rules use your income from two years prior. For example, your 2026 IRMAA determinations generally rely on your 2024 tax information. If your income fell because of a qualifying life-changing event, check whether Form SSA-44 allows you to request that Social Security use more recent income information.

18. You consider Roth conversions without a clear tax projection.

Example: “Roth is good” becomes “convert as much as possible.”

Cost: You might pay a high rate now to avoid a lower rate later.

Do this instead: Choose a target bracket, consider IRMAA, and convert only to the level that supports the broader plan. See “When a Roth Conversion Helps. And When It Doesn’t.”

19. You treat RMDs as a form-filling task instead of a planning lever.

Example: You take RMDs in December without thinking about withholding, giving, or timing.

Cost: Missed opportunities, avoidable stress, and possible underpayment penalties if you do not handle withholding or estimated taxes carefully.

Do this instead: Plan RMD timing earlier. Consider your withholding strategy and QCDs, as applicable.

20. You haven’t reviewed beneficiaries and account access recently.

Example: Your life changed, but you didn’t make any changes to your IRA beneficiaries or the transfer on death (TOD) settings for your taxable account.

Cost: Money may not go where you think it will, and access can get messy for survivors.

Do this instead: Review beneficiaries annually and after major events. Confirm who can access key information if you become incapacitated or pass away.

21. You don’t have a simple system for passwords and device security.

Example: The only person who knows logins is you, on one device. Or you have written your passwords down in multiple places, and the list is outdated, full of cross-outs, or hard to follow.

Cost: Cyber risk and administrative risk for you and your family. If something happens to you, your loved ones won’t know how to access your accounts. Worse, they might not even know some of your accounts exist.

Do this instead: Use an online password manager, enable two-factor authentication, and set emergency access.

How many signs are too many

If one or two of these signs apply, that’s normal. DIY investing involves uncertainty sometimes.

If you checked three to five, slow down before your next big move, especially if taxes or retirement withdrawals are involved.

If you checked six or more, consider getting a second set of eyes before your next major decision. Not because you can’t do it, but because the job may have gotten bigger than it looks.

What to do next

DIY investing can work. Many smart people do it well.

You may not need someone to take over. Sometimes, you need a better process, a tax projection, or a second opinion before a major move.

The problem is not intelligence. The problem is that the job quietly gets bigger. As retirement gets closer, investing becomes less about what you own and more about how you draw it down. That’s where taxes show up.

Start with the next decision in front of you. Before you act, ask: What are the tax consequences? What account is affected? What happens if markets move against me?

Next, I’m returning to my tax series, which will continue to focus on how DIY investing mistakes quietly become tax mistakes. The kind that show up as surprise capital gains, IRMAA surcharges, inefficient withdrawal order, or poorly timed Roth conversions.

In my next post, I’ll focus on an easier way to handle estimated tax payments in retirement, including techniques that may simplify the process and reduce the risk of underpayment penalties.

Download

If you want a companion checklist, I created a one-page download:

DIY Investor Self Check. 21 DIY investing mistakes that may be costing you more than fees.

FAQ

How do I use this list without overreacting?

Use it as a signal, not a verdict. If you check a few boxes, pick one area to improve this month. Write your rebalancing rule, define your cash buffer, or run a simple tax projection before you sell.

If I want to stay DIY, what are the two highest-leverage upgrades?

First, write your rules for buying, selling, and rebalancing so your emotions don’t take over. Second, run a tax projection before big moves, especially in the five years before and after retirement.

Which tax landmines most often catch DIY investors?

The DIY investing mistakes I see most often involve income stacking (implementing too many different tax planning strategies in the same year), surprise capital gains, wash sales across accounts, Roth conversions without bracket targets, and Medicare surcharges that appear two years later.

How do I know if someone is actually a fiduciary?

Ask for it clearly and ask what standard they operate under. If you want a deeper explanation and questions to ask, see the related post “Work With a Fiduciary Adviser. It Matters.” (Link below.)