When Doing Your Own Taxes Costs More Than Hiring Help

For a lot of people, doing their own taxes makes perfect sense. If you're earning W-2 income, filing jointly, and taking the standard deduction, there's honestly not a lot you can get wrong. Tax software handles that kind of return well, and the risk of a costly mistake is low.

But complexity has a way of creeping in. It might start with a backdoor Roth conversion. Then a brokerage account leads to investing mistakes. Maybe a decision to file separately for student loan purposes, or a practice generating 1099 income on top of your W-2. Each one, on its own, feels manageable. But stacked together, they create interactions between forms, rules, and timing decisions that tax software doesn't flag and most people don't think to check.

Overpaying taxes isn't an intelligence problem. It's a coordination problem. And it tends to show up in a few predictable places.

Retirement account rules that reach further than you think

One of the first signs a tax situation has outgrown DIY is when strategies that seem simple on their own start creating problems you didn't expect. Retirement account contributions are a common culprit.

Backdoor Roth conversions and the pro rata rule

The backdoor Roth conversion is a perfect example of a strategy that feels simple but is one of the easiest to get wrong without realizing it.

The mechanics are straightforward: contribute to a traditional IRA, convert to a Roth. But the IRS has something called the pro rata rule, and it looks at all of your IRA balances (traditional, rollover, SEP, SIMPLE) as one combined bucket. If any pre-tax money is sitting in any of those accounts, a proportional share of your conversion becomes taxable. This is the pro rata rule, and it catches people all the time.

And if nobody files Form 8606 to track the cost basis, which we see missing from client returns constantly, the record-keeping problem compounds for decades. You could end up paying tax on the same dollars twice: once at conversion and again when you take distributions in retirement.

Direct Roth contributions when your income changes mid-year

The other Roth mistake we see constantly is more of a timing problem. For 2026, the ability to contribute directly to a Roth IRA phases out between $153,000 and $168,000 for single filers and between $242,000 and $252,000 for married filing jointly. If you're filing separately, the phase-out is $0 to $10,000, which means virtually anyone filing separately and working in a professional setting is over the limit.

The trouble is that income isn't always predictable. A raise, a strong production year, or a mid-year decision to file separately for student loan purposes can push you over the threshold after you've already contributed directly. If you don't catch it and fix it before filing, a 6% excise tax applies every year the excess sits in the account.

The precautionary move for 2026: if there's any chance your income will cross those thresholds (or any chance you'll file separately), just do the backdoor Roth from the start. A couple of extra steps up front is far easier than unwinding an excess contribution later.

Your default brokerage account settings are making decisions for you

When you sell shares in a taxable brokerage account, the IRS needs to know which shares you sold, because each purchase — each “lot” — has a different cost basis and holding period. 

Most platforms default to FIFO (first in, first out) or average cost. FIFO sells your oldest shares, which typically carry the most growth and generate the largest taxable gain. Average cost isn't much better.

The smarter approach is specific identification (spec ID), which lets you choose exactly which lots to sell, prioritizing shares with less appreciation or even those at a loss. That one setting change can meaningfully reduce the tax hit on every sale. But it's not something tax software prompts you to think about, and it's not something most people know to look for.

This also connects to tax-loss harvesting, which is intentionally selling positions that are down to capture losses you can use against future gains. You can deduct up to $3,000 in net capital losses per year ($1,500 if married filing separately), and unused losses carry forward indefinitely. For practice owners planning a future business sale, or homeowners sitting on significant property appreciation, building up harvested losses over the years can offset a major taxable event later.

But harvesting has its own trap. Buy something substantially similar 30 days before the sale, the day of the sale, or 30 days after the sale, and you may get an IRS notice that disallows the loss entirely under the wash sale rule. That's another area where knowing the rule exists isn't enough. You need to execute it correctly, every time.

Charitable giving that's generous but not strategic

If you're already donating to causes you care about, and many high-income professionals are, the question isn't whether to give. It's whether your approach to giving has kept pace with everything else in your financial picture.

Two adjustments make a meaningful difference:

• Donating appreciated shares instead of cash: You get a deduction for the full market value, neither you nor the charity pays capital gains on the appreciation, and it helps rebalance your portfolio at the same time. A donor-advised fund (DAF) makes this easy to manage — you contribute the shares, take the deduction now, and distribute to your chosen charities over time.
• Bunching contributions: With the SALT deduction cap rising to $40,400 for households under $505,000 in AGI for 2026, more taxpayers may find themselves near the itemization threshold. Bunching means making two or three years' worth of charitable gifts in a single year to clear that threshold, then taking the standard deduction in the off years. Total giving stays the same, but the timing gets more strategic.

One note for married couples filing separately: if one spouse itemizes, the other must, too. So the decision to itemize needs to work for both returns.

You're self-employed and estimating as you go

The IRS operates on a pay-as-you-go system, and if your taxes aren't being withheld through a payroll provider, you're the one responsible for making quarterly estimated tax payments. Get the amounts wrong, and the IRS charges underpayment penalties. This happens even if you're owed a refund for the year.

The safe harbor rule is worth knowing: pay at least 110% of your prior-year tax liability (100% if your AGI is under $150,000), and you'll avoid penalties. If you also want to avoid interest, you'll need to estimate closer to your actual current-year liability, which is genuinely hard for business owners with uneven income.

Quarterly due dates are:

• April 15
• June 15
• September 15
• January 15 of the following year

States may have different schedules, so check yours. And if you do get hit with a penalty, first-time penalty abatement may be available if you have reasonable cause and a clean compliance history, though the IRS almost never waives interest.

When tax planning works in a silo, money gets lost

Even people who hire a CPA can run into coordination problems if their tax professional is working in isolation from the rest of their financial plan. And for DIY filers, the risk is even higher because there's no one checking how one decision ripples into another.

Here are a few examples we see all the time: 

• A CPA files a married couple jointly without realizing that filing separately would save thousands on student loan payments. 
• A tax professional recommends a SEP IRA without knowing it triggers the pro rata rule on backdoor Roth conversions — when a solo 401(k) would have avoided the issue entirely. 
• A borrower who could have filed a tax extension to delay higher income from hitting their IDR recertification files on time by default, and their monthly payment jumps by hundreds of dollars. 
• A W-2 employee sets up an S-corp on the advice of social media without any real benefit, just added complexity and compliance cost. 
• Someone filing separately doesn't fully complete their itemized deductions, leaving money unclaimed.

None of these is rare. They happen because tax planning is treated as its own silo, disconnected from student loans, investment strategy, retirement planning, and cash flow. The filing itself might be accurate. The strategy behind it is where the money gets lost.

How to know if it's time to get help

Tax mistakes compound. A missed form this year becomes a record-keeping problem five years from now. A default setting you never changed costs you a little more on every trade. A filing status decision made without considering your loans can cost five figures over a repayment period.

If any of the following describe your situation, your taxes probably have enough moving parts to warrant professional coordination:

• You have student loans on an income-driven repayment plan.
• You're doing or should be doing backdoor Roth conversions.
• You're filing married separately for strategic reasons.
• You own a practice or have self-employment income.
• You have a taxable brokerage account with meaningful unrealized gains.
• You've had a major life change this year, such as new income, a new baby, marriage, or relocation.

Getting proactive doesn't mean doing more work every month. It means making sure the decisions you're already making aren't quietly working against each other. That's exactly the kind of conversation we have with clients every day at SLP Wealth — connecting tax, student loan, and financial planning strategy into one coordinated plan. If you're not sure whether your current approach is costing you, reach out today to find out.

Sim Terwilliger, CFP®, CSLP®, contributed to this article.