Solo 401(k) Profit Sharing: How Business Owners Save $70K+ in Taxes in 2026
You're a surgeon earning $520,000 a year at the hospital. You max your 401(k) at $23,500. You feel good about it. You tell yourself you're doing everything right.
And then April comes, and you write a check to the IRS for $86,000.
What nobody told you: that $23,500 isn't your ceiling — it's your floor. If you have even one source of self-employment income — consulting for a medical device company, expert witness work, a small practice on the side, board seats — you can contribute more than triple that amount through a Solo 401(k) with profit sharing. Legally. Without a defined benefit plan. Without a team of actuaries.
Here's the part that stings: your CPA probably never mentioned it.
The $23,500 Ceiling (and Why It's Arbitrary)
If you're a high-income W-2 earner, your employer-sponsored 401(k) caps you at the employee deferral limit — $23,500 in 2026. You max it. You're done. That's what the box says.
But the moment you have any self-employment income — even $20,000 in 1099 consulting fees — a Solo 401(k) opens a second door. It lets you contribute in two capacities at once:
- Employee deferral: Up to $23,500 (the same limit, but from your self-employed earnings)
- Employer profit share: Up to 25% of your net self-employment income
When you combine both, the total contribution limit for 2026 is projected at $70,000 — nearly three times what you can do with a standard 401(k) alone.
And here's the kicker: you can have both an employer 401(k) and a Solo 401(k) for your side business. The employee deferral limit ($23,500) is shared across all plans, but the employer profit share is per business. That means you can max your W-2 401(k) deferral, then add a full profit-sharing contribution from your side business on top.
The Real Numbers: A $90,000 Example
Let's make this concrete. A surgeon in San Diego earns $520,000 from the hospital system. She also does $130,000 a year in consulting for two medical device companies — paid on a 1099.
What she does today: Maxes her hospital 401(k) at $23,500. Pays self-employment tax on the full $130,000. Writes a big check every April.
What she could do with a Solo 401(k):
| Component | Amount |
|---|---|
| Employee deferral (hospital 401k) | $23,500 |
| Employee deferral (Solo 401k — shared limit, already used) | $0 |
| Employer profit share (25% of $130,000 net) | $32,500 |
| Total tax-deferred in 2026 | $56,000 |
If her consulting business nets $280,000 (say she builds a speaking and advisory practice), the employer contribution jumps to $70,000 — hitting the plan maximum of $70,000 for the year.
Combined with her hospital 401(k) of $23,500, that's $93,500 in total tax-deferred contributions in a single year. From a single retirement plan structure her CPA never set up.
What that saves her in taxes:
At a 35% marginal federal rate plus 3.8% NIIT and California state tax (9.3%), every dollar contributed saves roughly 48 cents in combined taxes. On an additional $32,500 contribution, that's $15,600 in tax savings this year alone. Over a 10-year career, assuming 7% growth, that extra $32,500/year compounds to over $450,000 in additional retirement wealth.
Why Most CPAs Never Set This Up
There's a reason this strategy isn't common knowledge. It's not malicious — it's structural.
Most CPAs operate on a compliance model: they collect your documents in March, file your return in April, and disappear until next year. Setting up a Solo 401(k) requires:
- Knowing you have self-employment income (your CPA might not ask)
- Drafting a written plan document before December 31
- Calculating the profit-sharing contribution correctly
- Coordinating the employee deferral limit across two separate plans
- Filing Form 5500-EZ once the plan hits $250,000
That's 10–15 hours of work a typical compliance CPA won't do unless you specifically ask. And most high earners don't know to ask.
The frustrating part: a $32,500 additional contribution in year one more than pays for the setup cost. It's a one-time lift for recurring, compound-return savings.
Solo 401(k) vs. SEP IRA vs. Defined Benefit Plan
If you're a business owner or side-income earner, you have options. Here's how to think about them:
SEP IRA — Simpler to set up, but the contribution is limited to 20% of net self-employment income (not 25%), and it counts against your ability to do a Backdoor Roth IRA because of the IRA aggregation rule. Good for simplicity, bad for high earners who also want Roth access.
Solo 401(k) — Higher contribution limit (25% as the employer), allows Roth deferrals, and doesn't interfere with Backdoor Roth IRAs. Requires a little more paperwork but offers significantly more contribution capacity.
Defined Benefit / Cash Balance Plan — The heavyweight option. Can shelter $200,000+ per year, but requires annual actuarial certification, ongoing contributions, and significantly higher administrative costs. Best for consistent $500K+ earners who want maximum deferral and are committed to the long-term funding obligation.
The Solo 401(k) is the sweet spot for most high earners with side income: high contribution capacity, moderate administrative lift, and full flexibility.
How to Set It Up Before Year-End
You have time — but not unlimited time. Here's the timeline:
Before December 31, 2026: You must adopt the Solo 401(k) plan document. This means working with a provider (Vanguard, Fidelity, Schwab, or a TPA for a customized document) to establish the plan. The plan must exist before the end of the tax year.
By Tax Day 2027 (April 15, 2027): You can make the employee deferral election and the employer profit-sharing contribution for the 2026 tax year.
Pro tip: The best time to set this up is now — before Q4. You want to calculate your projected self-employment income with enough runway to adjust your quarterly estimated tax payments. Every dollar you contribute to the Solo 401(k) reduces your taxable income, which means you can lower your Q3 and Q4 estimated payments accordingly.
Most business owners wait until December, scramble to find a provider, and either rush the document or miss the window entirely. A 30-minute conversation in July saves a headache in December.
If you're ready to go further — for example, if your self-employment income is $300K+ and you want to shelter even more — a defined benefit/cash balance plan can push contributions past $200,000 a year. Or if your employer 401(k) allows after-tax contributions, the mega backdoor Roth strategy lets you convert those contributions to Roth. The Solo 401(k) is the entry point; these are the next levels.
Ready to find out what your side income could be doing for your retirement?
Book a free 30-minute strategy session with Roadmap Tax. No obligations. No pitch. Just a straightforward conversation about what you're leaving on the table — and what to do about it.
Phone: (619) 280-2700
Email: info@RoadmapTax.com
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FAQ
What is a Solo 401(k)?
A Solo 401(k) is a retirement plan designed for self-employed individuals and business owners with no full-time employees (other than a spouse). It allows both employee salary deferrals and employer profit-sharing contributions, with total limits up to $70,000 in 2026.
Can I have a Solo 401(k) if I already have a 401(k) through my employer?
Yes. The employee deferral limit ($23,500) is shared across all plans, but you can make employer profit-sharing contributions from your self-employment income on top of what you contribute to your employer plan. Many high earners maintain both.
How much can I contribute to a Solo 401(k) with profit sharing?
The total limit for 2026 is projected at $70,000 (employee deferral of $23,500 plus employer profit share of up to 25% of net self-employment income, capped at the overall limit). If you're 50 or older, a $7,500 catch-up contribution may also apply.
Do I need employees to set up a Solo 401(k)?
No. A Solo 401(k) is specifically designed for self-employed individuals, sole proprietors, and single-member LLCs with no full-time employees. If you hire employees, you'll need a different plan type.
Is a Solo 401(k) better than a SEP IRA for high earners?
Generally yes for high earners. A Solo 401(k) allows higher contribution limits (25% vs 20% of net income), doesn't interfere with Backdoor Roth IRA contributions, and offers the option of Roth deferrals within the plan.
When do I need to set up a Solo 401(k) for the 2026 tax year?
The plan document must be adopted by December 31, 2026. Employer profit-sharing contributions can be made up to the tax filing deadline (April 15, 2027, plus extensions).
