Five tax mistakes that quietly cost high earners a fortune

A guy I’ll call Brian crossed the $600K income mark last year. Great year. New clients, a clean exit from a side business, a decent stock vest. He used the same accountant he’d used since his first freelance year. Come April, he got a call from that accountant that went something like this: “So, the bill is $87,000 more than last year. Also, there’s a penalty.”

Brian had done nothing wrong in his bookkeeping. His W-2 was clean. His 1099s were organized. His CPA had filed everything on time, the way she always did. The problem was that Brian had outgrown what his accountant was set up to deliver, and nobody had told him.

That conversation happens to high earners constantly. The mistakes below are the ones I keep seeing people at $500K+ income levels make, year after year, often without realizing they’re making them. A few don’t become visible until the bill lands. Most are fixable if caught early.

Why high earners need tax strategy, not just tax prep

Here’s the first thing worth saying out loud: filing taxes and planning taxes are two different jobs.

Most accountants are compliance-focused. They take the numbers you hand them, enter them in the right boxes, and hit submit. That’s tax preparation. It’s a necessary service. It’s also not what saves a high earner money. The work that actually moves the needle happens in September, not April. It happens when someone is looking at your projected income, your entity structure, your retirement contributions, and your estimated payments, and asking: what can we still change this year?

That’s tax strategy. It requires year-round contact. It requires a firm that bothers to ask what your income looks like before it’s finalized, not after. For clients in the high-earner bracket, working with a firm like K&R Strategic Partners, which handles strategic planning alongside compliance, is the point at which the relationship stops being transactional and starts producing real savings.

The gap between these two approaches tends to be expensive. I’ve watched people pay an extra five figures in avoidable tax simply because nobody flagged a timing issue in October, or pointed out that a 1099 consulting gig had pushed them into a different bracket with a different set of planning options.

None of what follows works if this gap isn’t closed. You can read every tax article on the internet, but if the relationship with your CPA is still built around a once-a-year document drop, the information won’t get applied.

Mistake 1: Ignoring the AMT and the estimated tax penalty

Two quiet drains on high-earner cash flow almost never get mentioned until they’ve already hit.

The first is the Alternative Minimum Tax. The AMT was built decades ago to stop high-income taxpayers from using too many deductions to zero out their federal bill. After the 2017 Tax Cuts and Jobs Act, fewer households trigger it than before. But it still catches people with large incentive stock option exercises, certain deductions in high-tax states, and specific kinds of investment income. If you exercised ISOs and didn’t sell the shares in the same calendar year, the AMT is probably in play whether you know it or not.

The second is the estimated tax underpayment penalty. If you have income outside of a W-2 (consulting, K-1 distributions, capital gains, rental income, RSUs that vest at the wrong time), you’re supposed to be making quarterly estimated payments. Miss them, underestimate them, or pay late, and the IRS adds a penalty. The current rate has hovered around 8% recently. That’s not a rounding error. The IRS provides full guidance on estimated taxes for anyone who wants to read the actual rules.

What makes both of these sting is that they’re preventable. A decent projection in October catches them. A bad projection, or no projection at all, lets them compound. I’ve seen clients hand $4,000 to $9,000 in penalties and AMT spillover back to the federal government every single year because nobody ran the numbers in time. At $600K+ income, that’s a fully paid vacation. Annually. Just vanishing.

Mistake 2: Leaving the entity structure on autopilot

If you’re earning high-six or seven figures through a business (consulting, professional practice, content, e-commerce, agency), the structure you chose when you were making $120K might be actively costing you now.

The most common version of this is the solo freelancer or consultant still operating as a sole proprietor, or as a single-member LLC taxed as one. Every dollar of profit hits self-employment tax on top of income tax. Switching to an S-Corp election can shift part of the income to a reasonable salary, with distributions not subject to self-employment tax. The math isn’t automatic, and the “reasonable salary” test has real teeth. For a consultant clearing $300K in profit, the savings typically land in the $10K to $25K range annually.

The other common version is the business owner stuck in a C-Corp because that’s what the attorney defaulted to at formation. Post-TCJA, C-Corps have a flat 21% federal rate, which sounds appealing until you remember that the owner still pays tax again on dividends. Pass-through entities with the Qualified Business Income deduction often work better for service businesses, depending on specialty.

Entity decisions are not one-time choices. They should be revisited every few years, especially after a major income jump, the addition of a partner, an investor coming in, or a move into a new line of business. Reasonable CPAs reopen this conversation every 24 to 36 months. Most high earners I meet haven’t had their entity structure examined in a decade. That’s not a drafting error. That’s someone paying tax at a higher rate than they need to, indefinitely.

Mistake 3: Getting casual about state residency

State tax is where high earners get ambushed.

California, New York, New Jersey, Hawaii, Oregon, and Minnesota all have top marginal rates above 9%. If you earn $800K in California, your state tax bill alone can run north of $90,000. People in those brackets sometimes decide to “move” to Texas, Florida, Tennessee, Nevada, or Washington. The idea: no state income tax, lower federal residency audit risk, done.

It’s almost never that simple.

State residency is a legal concept built on facts, not intent. Owning a home in the new state is one data point. Where your family lives, where your doctor is, where your dog is, where you vote, where your mail goes, which state’s driver’s license you carry, how many days a year you physically spend in each place. All of these are data points. California and New York in particular run aggressive residency audits. They’ll pull cell phone tower data, credit card statements, and E-ZPass records to build a case that you’re still a resident no matter what address is on your driver’s license.

High earners who get this wrong often end up paying tax in two states at the same time. The “easier” fix, spending 183 days in the new state, isn’t actually enough on its own if the old state still considers you domiciled there. I’ve seen people carry dual-state tax exposure for three years before their CPA noticed, because nobody asked the right questions at the moment of the move.

The celebrity version of this story is well documented. The Willie Nelson and Wesley Snipes cases are the famous ones, but the more common variety involves somebody making $1.5M who thought a Miami condo solved their New York problem. It didn’t.

Mistake 4: Leaving retirement account room on the table

High earners are often told they’ve “phased out” of the obvious retirement accounts. The Roth IRA income limits hit. Direct traditional IRA deductions phase out. The story stops there. It shouldn’t.

If you have self-employment or 1099 income on the side, a Solo 401(k) lets you contribute up to the federal limit on the employee side and put an additional 25% of net self-employment income on the employer side. For a consultant pulling in $250K in 1099 work, that combination can approach $70,000 in pre-tax savings in a single year. The account itself costs roughly nothing to open at Fidelity, Schwab, or Vanguard.

If you’re further along and running a profitable professional practice, a defined benefit plan (sometimes bundled with a cash balance plan) can shelter significantly more. For a 50-year-old dentist clearing $700K, well-designed plans routinely allow annual contributions in the $150K to $250K range, all pre-tax. These have administrative costs and funding obligations, but the math for the right profile is not close.

For W-2 earners, the backdoor Roth strategy is still available (pending future legislation), and the mega backdoor Roth, if your employer’s 401(k) plan allows after-tax contributions with in-service distributions, can move $30K-plus per year into Roth space on top of the regular contribution. Most people don’t know whether their employer plan supports it. The answer is usually in the Summary Plan Description.

None of this is exotic. It’s all well-documented territory that gets missed because nobody sat down with the client and mapped out the available shelters against actual income.

Mistake 5: Focusing only on the tax bill, not the cash flow around it

The last mistake is the most common and the most subtle.

High earners tend to fixate on the bottom-line tax owed. That number is visible. It arrives on a form, it’s clean to read, and it’s easy to benchmark. What’s harder to see is the cash flow timing around that number, which often matters more.

Bunching charitable deductions into a single year using a donor-advised fund can push you above the standard deduction threshold in one year, letting you take the larger itemized deduction, rather than spreading smaller gifts across several years where none of them clear the threshold. Fidelity Charitable, Schwab Charitable, and Vanguard Charitable all run donor-advised funds that a CPA can help set up in an afternoon.

Harvesting capital losses in December to offset realized gains earlier in the year is another one that gets missed. So is the timing of when to exercise non-qualified stock options, when to take a Roth conversion in a lower-income year, and when to accelerate or defer income across a calendar boundary to stay under a phase-out threshold.

These are small moves individually. Added together, across a five-year window, they’re the difference between a high earner keeping an additional $100K and handing it to the federal government. None of them require aggressive positions. All of them require someone paying attention before December 31.

The common thread across every mistake in this list is timing. Taxes get filed once a year. Tax strategy is a year-round process. Treating it as a once-a-year task is where the money quietly leaks out.

What to actually do about it

If any of this sounds familiar, the first move is not to switch accountants immediately. It’s to have one honest conversation with your current one. Ask three questions: what’s my projected tax bill this year, what can we still change before December, and is my entity and retirement account setup actually optimized for my current income?

If the answers come back vague, or if the response is “let’s revisit at tax time,” you’ve diagnosed the problem. A CPA or firm set up for strategic work will have concrete answers, usually before you finish asking the question. That’s the relationship worth keeping, and it’s the one worth building early in the year, not the week before the April deadline.