Most business owners still think retirement means "I'll throw something in an IRA if I remember."
If you're making real profit, that habit leaves a pile of money exposed every year. A Solo 401(k) (also called an individual 401(k)) is one of the cleanest ways for owner-only businesses to shelter a lot more, legally, while you still control the company.
This isn't magic. It's a retirement plan designed for businesses with no full-time employees other than the owner (and spouse, in many setups). Employee + owner thinking shows up here the same way it does with an S-corp: the IRS treats paycheck money and profit money differently, and the plan rules follow that split.
Who a Solo 401(k) is actually for
You're generally in the lane if:
- You run a business with no employees who would have to be covered (spouse-as-employee rules can be friendly; random W-2 staff usually is not)
- You have earned income from the business (Schedule C profit, or W-2 wages from your S-corp, depending on structure)
- You want higher contribution room than a plain IRA
Not a fit (yet) if:
- You have a team that would force a full employer plan design
- Profit is thin and you'd be funding a plan with money you need for payroll and rent
- You're under the "make more first" stage and advanced sheltering is a distraction
Under ~$400K, get structure and basics right. A Solo 401(k) can still make sense earlier when profit is steady. Just don't treat it like a flex if cash flow is fragile.
How the savings actually work
Think of two buckets inside one plan:
- Employee deferral: money you contribute as the worker (from wages or self-employment earnings, depending on entity)
- Employer contribution: money the business contributes as the boss, based on eligible compensation / net earnings rules
Together, those buckets can reach a much higher annual ceiling than a standard IRA. Limits change by year and age (catch-up rules exist). The point isn't memorizing a meme number. The point is modeling your pay and profit against the real IRS limits for the year you're in.
Example: An S-corp consultant takes a $120K reasonable salary and has leftover profit. They max the employee deferral from wages, then add an employer contribution based on that salary. Compared with "I might do $7K in an IRA," the difference can be tens of thousands sheltered in one year. Same business. Different keep.
A tax plan is like a personal trainer's workout. The Solo 401(k) is one of the heavy lifts. Someone still has to set it up, fund it on time, and keep the paperwork clean.
Solo 401(k) vs SEP IRA (plain English)
| Factor | Solo 401(k) | SEP IRA |
|---|---|---|
| Best for | Owner-only (or owner + spouse) shops | Simple owner plans, including some with employees (with coverage rules) |
| Employee deferrals | Yes (big part of the appeal) | No employee deferrals |
| Employer contributions | Yes | Yes |
| Setup complexity | More forms / plan docs | Usually simpler |
| Loans | Often available if plan allows | Generally not |
| Mega backdoor / Roth features | Possible depending on plan design | More limited |
SEPs are fine tools. Solo 401(k)s often win for high earners who can use both deferral and employer pieces. The table doesn't pick for you. Your wages, profit, and whether you have staff do.
Entity gotchas people skip
Sole prop / single-member LLC taxed as sole prop: Contributions tie to self-employment earnings after the right adjustments. Messy books = messy contribution math.
S-corp: Employee deferrals generally need W-2 wages. No salary, no deferral. This is why "I'll take all distributions and skip payroll" fights your retirement plan. See reasonable salary.
Partnerships / multi-member setups: Partner rules get picky. Don't copy a YouTube sole-prop example onto a three-owner LLC.
Deadlines: Establishing the plan and funding contributions are different clocks. Some funding can happen after year-end if the plan existed in time. Confirm your provider and year. Year-end planning is when this should get calendared, not discovered in April. We cover that rhythm in year-end tax moves.
Mistakes that blow the benefit
Mistake #1: Setting it up after you needed it.
You can't always rewind the calendar. If the plan had to exist by December 31, January enthusiasm doesn't fix it.
Mistake #2: Contributing more than the rules allow.
Overfunding creates cleanup problems. Limits are real.
Mistake #3: Ignoring the salary foundation in an S-corp.
Distributions aren't wages. Deferrals care about wages.
Mistake #4: Treating the plan like a checking account.
Early withdrawals, bad loans, and sloppy beneficiaries turn a tax tool into a tax problem.
Mistake #5: Buying a plan from a sales pitch without integrating tax + payroll.
The provider holds assets. Your advisor still has to fit contributions into salary, estimates, and cash flow.
Who should act now (and who should wait)
Act if:
- Owner-only (or owner + spouse) business with solid profit
- You're already past "IRA energy" contribution levels
- You have (or will set) clean payroll / books
- You want shelter that scales with income
Wait or keep it simpler if:
- Cash is tight month to month
- You're about to hire a team that changes plan design
- You're still figuring out whether the business is real
Make more before you obsess over saving more. When the profit is there, a Solo 401(k) is one of the tools regular people are supposed to use, the same way high earners always have.
The short version
- A Solo 401(k) is built for owner-only businesses that want more room than a basic IRA.
- Employee deferrals + employer contributions are the engine.
- S-corp owners usually need real W-2 wages to unlock deferrals.
- Setup timing and funding deadlines are not the same thing.
- SEP can be simpler. Solo often shelters more when you qualify.
- Model your numbers. Don't copy a stranger's contribution flex.
FAQs
What is a Solo 401(k)?
A 401(k) plan for a business with no employees other than the owner (and often a spouse). It combines employee-style deferrals and employer contributions in one plan.
Can I have a Solo 401(k) and an S-corp?
Yes. Many owners do. Deferrals generally come from W-2 wages. Employer contributions follow compensation rules. Payroll and the plan have to talk to each other.
Is a Solo 401(k) better than a SEP IRA?
Often for high earners who can use deferrals plus employer money. SEPs stay attractive for simplicity. Compare using your income, not a generic chart.
When do I have to set up the plan?
Rules depend on the year and plan type. Don't assume you can open it in April for the prior year. Confirm deadlines before year-end.
Can my spouse participate?
Often yes if they have earned income from the business and the plan allows it. That can increase household contribution room. Get the plan document right.
Does a Solo 401(k) reduce my tax bill dollar for dollar?
Pre-tax contributions reduce taxable income subject to the usual rules. The exact savings depends on your bracket, entity, and whether any Roth elections apply. It's real math, not a guarantee.
References
- IRS — One-Participant 401(k) Plans
- IRS — Retirement Plans
- IRS — SEP Plans
- IRS — 401(k) Contribution Limits
- IRS — Self-Employed Retirement Plans
What to do next
Owner-only business with real profit and a tiny retirement habit?
At CEOHAVEN, we help entrepreneurs and real estate investors with tax planning, tax preparation, and bookkeeping. You should know whether a Solo 401(k) fits your pay, profit, and timeline before another year slips.
Book a call. We'll look at your entity, contribution room, and what to set up before the next deadline.
It's not about how much you make. It's about how much you keep.