Ask what is a solo 401k and the short answer is a retirement plan built for exactly one person. It is a normal 401(k) stripped down for a business with no full-time employees other than the owner (and optionally a spouse). The twist that makes it powerful: you wear two hats, employee and employer, so you get to contribute from both sides of the same paycheck.
What changed in 2026
- Limits ticked up again. The IRS indexes both the employee deferral and the overall cap to inflation, so the 2026 numbers are higher than last year. Do not trust a figure from an old post — pull the current IRS number before you fund anything.
- Roth employer money is real now. SECURE 2.0 made employer contributions eligible to be Roth, and by 2026 far more providers actually support it. A solo owner can route the employer side to Roth, not just the employee deferral.
- A bigger catch-up for ages 60 to 63. The "super catch-up" for that narrow age band is in effect, letting those savers defer more than the standard 50-plus catch-up. Confirm your exact age eligibility and the current amount.
- Roth catch-up for high earners. For workers above a wage threshold, catch-up contributions may have to go into Roth rather than pre-tax. This continues to phase in, so check how it applies to you.
Who actually qualifies
You need self-employment income and, crucially, no full-time W-2 employees other than yourself and a spouse. A freelancer, a one-person LLC, a consultant, or someone with a serious side gig all count — even if you also have a day job with its own 401(k).
- A spouse can join the same plan if they earn income from the business, effectively doubling household contribution room.
- Part-timers usually do not break it if they work under roughly 1,000 hours a year, but the rules around long-term part-time workers have tightened, so watch this if you scale up.
- A W-2 job elsewhere is fine. Your employee deferral limit is shared across all 401(k)s you are in, but the employer profit-sharing side is separate.
The two-hats math
This is the whole appeal. You contribute in two ways:
- As the employee — a salary deferral up to the annual IRS limit (this is the number shared with any other 401(k) you have).
- As the employer — a profit-sharing contribution, generally up to around 20 to 25 percent of net self-employment income, depending on your business structure.
Add both together and you hit a combined ceiling that is far above what an IRA allows. The exact percentages differ for a sole proprietor versus an S-corporation, so run your specific numbers or ask a tax pro — do not eyeball it.
How it compares
| Feature |
Solo 401k |
SEP-IRA |
SIMPLE IRA |
| Employee deferral |
Yes |
No |
Yes (lower) |
| Roth option |
Often |
Rarely |
Limited |
| Best for |
High-income solo owners |
Simple, low-admin savers |
Small teams |
| Loans allowed |
Sometimes |
No |
No |
| Admin burden |
Moderate |
Low |
Low |
The solo 401k usually lets you contribute the most at a given income and adds a Roth choice, but it carries more paperwork. A SEP-IRA is the lazy-but-effective option if you want fewer moving parts.
Roth or traditional inside it
A solo 401k can hold pre-tax money, Roth money, or both. Pre-tax lowers this year's taxable income; Roth is funded with after-tax dollars and grows tax-free. Many self-employed people split the difference. If your income swings year to year, the flexibility to lean pre-tax in a fat year and Roth in a lean one is genuinely useful.
Pitfalls and what to skip
- The $250k form. Once plan assets cross roughly $250,000, you generally must file Form 5500-EZ each year. Miss it and penalties stack up fast.
- Deadlines are split. You typically must establish the plan by year-end but can fund it up to your tax-filing deadline. Confirm both dates each year.
- Do not ignore fees. Some providers charge setup and per-account fees that quietly eat returns; a plain low-cost brokerage plan is fine for most people.
- Skip the "checkbook control" pitch from promoters selling self-directed solo 401ks for crypto or real estate unless you truly understand the compliance load. For most savers it is expensive complexity you do not need.
FAQ
Can I have a solo 401k and a job with a regular 401(k)?
Yes. Your employee deferral limit is shared across both plans, but you can still make employer profit-sharing contributions to the solo plan on top.
What happens if I hire a full-time employee?
The plan generally has to convert to a standard 401(k) that covers eligible staff, which changes the rules and cost. Plan ahead if you expect to grow.
Is a solo 401k or a SEP-IRA better?
The solo 401k usually allows larger contributions at moderate incomes and adds a Roth option; the SEP-IRA is simpler with almost no admin. Match it to how much complexity you will tolerate.
Do I need an EIN to open one?
Yes, you generally need an Employer Identification Number for the business, which is free from the IRS and takes minutes to request online.
Where to go next
Retirement is one piece of the plan. If you are also saving for a kid, compare the best 529 plans for 2026. To keep your interest-rate math honest, read APR vs APY in 2026. And to decide how aggressively to invest what you contribute, see asset allocation by age in 2026.