Five Expensive Tax Mistakes High-Earners Make
When your income reaches a certain level, the structural decisions you made years ago start carrying real consequences. A few of them may be worth a second look.
Here are five mistakes I see over and over again with high-earning professionals, plus the simple fixes you can put in place immediately.
1. Roth 401(k) Contributions in the Top Tax Bracket
Roth accounts, which are tax-free accounts, almost always sound better than tax-deferred accounts. But if you’re in the top tax bracket, paying the highest possible rate today so you can stash your 401(k) with tax-free dollars often doesn’t make sense.
The Mistake: Making Roth 401(k) contributions while in the top marginal bracket just because “tax-free later” sounds good.
The Cost: You're paying the highest possible rate on every dollar going in. A traditional 401(k) is one of the most effective tools a W-2 employee has to reduce their current tax bill, and Roth contributions bypass that entirely. Worth noting: most employer matching contributions are tax-deferred regardless of how you contribute. So that Roth 401(k) that you have might not be 100% tax-free.
The Fix: If you’re at or near the top tax bracket, strongly favor traditional 401(k) contributions. If you want to build a Roth (tax-free) bucket, use backdoor Roth IRA contributions or see if your plan accepts after-tax contributions alongside your traditional contributions.
2. Filling Up Your HSA… and Draining It Immediately
A Health Savings Account is one of the rare “triple tax advantaged” vehicles you get. Using it like a checking account wastes its real power.
The Mistake: Maxing the HSA but swiping the HSA card for every prescription and co‑pay, so the balance never grows.
The Cost: You’re using your most tax‑efficient dollars to pay today’s bills, and your least tax‑efficient dollars to invest for later. Over 10–20 years, a fully invested HSA can turn into a six‑figure, tax‑free healthcare fund in retirement.
The Fix: If you can afford it, pay current medical costs from cash flow and invest the HSA in a long‑term portfolio. Save receipts so you preserve the option to reimburse yourself tax‑free down the road.
3. Rolling an Old 401(k) into an IRA and Killing Future Backdoor Roth Contributions
The 401(k) rollover‑to‑IRA is the popular, easy, default move… that quietly shuts a door many high‑earners wish they had later.
The Mistake: Leaving a job and rolling your 401(k) into a traditional IRA before considering other options.
The Cost: Once you have a large pre‑tax IRA, the backdoor Roth IRA strategy becomes messy because of the pro‑rata rule. I have covered the pro-rata rule in the past, without going into too much detail, a large IRA balance can create mostly taxable backdoor Roth conversions rather than the tax-free one you were planning for.
The Fix: Before you roll anything, ask: “Will I want to do backdoor Roth contributions in the future?” If yes, consider rolling the old 401(k) into your new employer’s 401(k) instead of an IRA, so your traditional IRA balance stays clean and keeps tax-free backdoor Roth IRA contributions on the table.
4. Treating Your Brokerage Account Like a Casino
Many high-earners build up sizable taxable accounts over the course of their careers. This taxable bucket is great because it gives you the most flexibility. The problem is when that account turns into a playground.
The Mistake(s): Frequent trading, hot tips, locking up funds in a private investment, focusing on pre-tax returns, and no real plan for gains or losses.
The Cost: Frequent trading leads to high turnover, and short‑term gains get taxed at ordinary income rates. Investing in private deals can lock up your capital for years, which undermines the “flexibility” that makes a taxable account valuable in the first place. Chasing yield often increases your tax burden, because many high‑yield dividend or interest investments are taxed as ordinary income at your top rate.
The Fix: Treat your taxable account like a long-term engine, not a slot machine. Design a well diversified, low cost portfolio that you can stick with. Keep trading minimal and intentional, and aim to rebalance on a regular cadence that takes advantage of those lower long-term capital gains tax rates when you do realize gains.
5. Holding Employer Stock Too Long in the Name of “Skin in the Game”
Equity comp is real pay. But a lot of people treat it like a loyalty test.
The Mistake: Letting RSUs or stock options vest, then holding the shares indefinitely because “I should have skin in the game.”
The Cost: You’re already concentrated in your employer through your salary and career risk. Stacking a big stock position on top of that amplifies single‑company risk, and it doesn’t undo the taxes you’ve already paid at vesting or exercise. If the stock drops, you feel the pain twice on your income and your portfolio.
The Fix: Decide in advance on a selling framework, for example “When RSUs vest, I sell most or all and reinvest in a diversified portfolio.” That treats equity like the compensation it is, not a bet you’re obligated to keep making.
None of these mistakes mean you’ve done anything wrong or broken any rules. They usually come from being busy, making reasonable choices with limited information, and defaulting to whatever seems easiest in the moment. If you review your own situation with these five areas in mind and discuss potential changes with a qualified tax or financial professional, you may be able to improve your long‑term outcomes in a way that gives you peace of mind.
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