Solo 401(k) vs. SEP-IRA: The Self-Employed Retirement Tax Strategy That Saves More

The Self-Employed Tax Reality

When you work for an employer, payroll taxes are split: you pay 7.65% and your employer pays 7.65%. When you're self-employed, you pay both halves — a total of 15.3% in self-employment (SE) tax on your net earnings. On top of that, you owe federal and state income tax. The combined effective tax rate for a self-employed person in the 22% bracket can easily exceed 37% on the marginal dollar.

That's the challenge. The opportunity is that self-employed workers also have access to a remarkably rich set of deductions and retirement vehicles that employed workers simply don't have. With deliberate planning, the self-employed can dramatically reduce what they owe.

Understanding Self-Employment Tax

Self-employment tax is composed of two parts:

• Social Security: 12.4% on net self-employment income up to $176,100 in 2025 (the Social Security wage base).
• Medicare: 2.9% on all net self-employment income, with no earnings cap.
• Additional Medicare Tax: An extra 0.9% on net self-employment income exceeding $200,000 (single) or $250,000 (married filing jointly).

Here's an important offset: you can deduct one-half of your total SE tax as an above-the-line adjustment to income. This deduction reduces your AGI — which in turn can reduce income tax and affect other income-based calculations — but it doesn't reduce your SE tax itself. On $100,000 of net self-employment income, SE tax is approximately $14,130 (92.35% × $100,000 × 15.3%), and you can deduct $7,065 from your gross income.

Maximizing Business Deductions

Business deductions are the most immediate lever to reduce net self-employment income — which reduces both income tax and SE tax simultaneously. The IRS allows deductions for expenses that are "ordinary and necessary" for your business. Common ones include:

• Home office: If you use a dedicated space exclusively and regularly for business, you can deduct it using the simplified method ($5/sq ft, up to 300 sq ft = $1,500 max) or the regular method (actual proportional expenses).
• Business mileage: $0.70 per mile in 2025 for business driving. Keep a mileage log — the IRS requires documentation.
• Equipment and technology: Computers, cameras, software subscriptions, phones used for business — all potentially deductible, with immediate expensing or depreciation schedules.
• Health insurance premiums: If you are not eligible for employer-sponsored coverage through a spouse, you can deduct 100% of your health insurance premiums (including dental and vision) as an above-the-line deduction directly from AGI. This is one of the most valuable deductions for self-employed workers.
• Professional development: Courses, certifications, industry publications, and professional memberships relevant to your work.
• Business travel and meals: Travel to client sites, conferences, and business meetings. Meals are generally 50% deductible when business is the primary purpose.
• Retirement plan contributions: Treated as a business deduction (more on this below).

Retirement Accounts: Your Biggest Tax Lever

Self-employed workers can shelter substantially more income from taxes through retirement accounts than most employees realize. The two main options:

SEP-IRA (Simplified Employee Pension): Allows you to contribute up to 25% of net self-employment income, capped at $69,000 in 2025. Contributions are 100% deductible. The SEP-IRA is simple to open, has no ongoing plan documents, and you can contribute until your tax filing deadline (including extensions). The main limitation: the same 25% contribution rate must apply to all eligible employees if you hire.

Solo 401(k): For those with no employees other than themselves (and possibly a spouse). Allows two types of contributions:

• Employee deferral: Up to $23,500 (2025), plus $7,500 catch-up if 50+. This is the "employee" portion and isn't limited by income percentage.
• Employer profit-sharing: Up to 25% of net self-employment income, totaling no more than $69,000 combined.

The Solo 401(k) is typically superior for moderate-income earners because the employee deferral amount can be larger than the SEP-IRA contribution at the same income level. For example, at $60,000 of net SE income, a SEP-IRA allows a $15,000 contribution, while a Solo 401(k) allows up to $23,500 in employee deferrals plus employer contributions.

Both accounts allow Roth options (though Roth SEP-IRA was only introduced in 2023, and not all institutions offer it). Choosing between traditional (deductible now, taxable later) and Roth (no deduction now, tax-free later) depends on your current vs. expected future tax bracket.

Managing Quarterly Estimated Taxes

Without employer withholding, self-employed workers must pay taxes on a quarterly schedule. In 2025, the deadlines are:

• Q1 (Jan–Mar income): April 15
• Q2 (Apr–May income): June 16
• Q3 (Jun–Aug income): September 15
• Q4 (Sep–Dec income): January 15, 2026

Underpaying estimated taxes triggers an interest-based underpayment penalty — even if you file and pay the full balance on time in April. To avoid the penalty, you can use either the safe harbor method (pay 100% of last year's tax, or 110% if AGI > $150,000) or the annualized income method (calculate taxes on actual income each quarter, useful for uneven income patterns).

The QBI Deduction for Pass-Through Income

The 2017 Tax Cuts and Jobs Act created a significant deduction for self-employed workers and pass-through business owners: the Qualified Business Income (QBI) deduction, also called the Section 199A deduction. It allows eligible self-employed individuals to deduct up to 20% of their qualified business income from federal taxes.

This deduction is subject to income limitations and restrictions for certain "specified service trades or businesses" (SSTBs) — such as law, consulting, and financial services. The phase-out begins at $197,300 for single filers and $394,600 for married filers in 2025. If your income is below these thresholds, the QBI deduction is generally available in full.

The QBI deduction is scheduled to expire at the end of 2025 under current law unless Congress acts to extend it — making 2025 potentially the last year to benefit from this significant tax break.