SEP IRA and Solo 401k are the two retirement plans self-employed owners reach for first, and picking the wrong one either buries you in paperwork or caps your savings below what you could have sheltered. Here's how the two compare for a business owner weighing options in 2026.
- Solo 401k wins for owner-only businesses that want the highest contribution ceiling and a plan loan option.
- SEP IRA wins on paperwork — no annual IRS filing, fund it as late as your extended tax deadline.
- SIMPLE IRA fits owners with W-2 employees who want a lower-cost, mandatory-but-capped employer plan.
- Solo 401k allows catch-up contributions for savers 50 and older; SEP IRA has no catch-up provision at all.
- Contribution dollar limits change every year — confirm current 2026 figures on IRS.gov before you fund an account.
Why this matters
Running your own business means you're both the employer and the employee, and nobody is automatically setting aside money toward retirement on your behalf. Self-employment tax runs 15.3% on top of income tax, so the account you pick to shelter savings has to pull real weight against that.
SEP IRA vs Solo 401k is the comparison most business owners run into first, because both let a sole proprietor, single-member LLC, or small S-corp owner set aside pre-tax dollars without sponsoring a full employer plan. Vital Investment Management works through this decision with business owners as part of fee-only financial planning — not as a pitch for a specific custodian or account provider.
The mechanics differ enough between the two that the wrong pick either adds filings you didn't need or shrinks your contribution room below what was available.
What makes the best self-employed retirement plan
- Contribution ceiling relative to net income — how much of what you actually earn you can shelter.
- Administrative burden — setup paperwork, annual filings, ongoing recordkeeping.
- Employee coverage rules — whether hiring W-2 staff forces contributions on their behalf.
- Catch-up eligibility — whether savers 50 and older can add extra.
- Loan and Roth access — whether you can borrow against the balance or designate Roth dollars.
- Deadline flexibility — how late you can open and fund the account for a given tax year.
SEP IRA vs Solo 401k at a glance
| Plan | Best For | Standout Feature | Key Limitation |
|---|---|---|---|
| Solo 401k | Owner-only businesses maximizing contribution room | Employee + employer contribution structure, catch-up eligibility, loan option | Form 5500-EZ required once assets pass $250,000; salary deferrals generally must be elected by December 31 |
| SEP IRA | Owners who want the least paperwork | No annual IRS filing; can be funded as late as the extended tax deadline | No catch-up contributions; must cover eligible employees at the same percentage as the owner |
| SIMPLE IRA | Owners with employees who want a lower-cost plan | Mandatory but capped employer contribution, lighter setup than a full 401k | Lower elective deferral ceiling than a 401k; steeper early-withdrawal penalty in the first two years |
1. Solo 401k: best for owner-only businesses maximizing contribution room
A Solo 401k (also called an individual 401k or one-participant 401k) works because you contribute in two roles: as the employee making an elective deferral, and as the employer making a profit-sharing contribution. Stacking both roles is usually why a Solo 401k lets an owner shelter more of their net self-employment income than a SEP IRA at the same earnings level. The plan only works cleanly if you — and a spouse on payroll, if applicable — are the only people working for the business; bring on a full-time common-law employee and the plan generally has to extend coverage to them too.
Solo 401k pros:
- Two contribution paths (employee deferral plus employer profit-sharing) instead of one
- Catch-up contributions available for savers 50 and older, with a higher "super catch-up" band for ages 60–63 under current law
- Optional loan provision — you can borrow from your own balance instead of taking a taxable distribution
- Roth option available at most custodians, so pre-tax and after-tax savings can be split
Solo 401k cons:
- Setup requires a plan document, not just an account application — more paperwork upfront
- Once plan assets pass $250,000, the IRS requires an annual Form 5500-EZ filing
- Salary deferral elections generally have to be made by December 31, so you can't decide in April how much to defer for the prior year
Best for: owners with no common-law employees who want the highest contribution ceiling and the option to borrow against the account.
Solo 401k verdict: Buy if you run the business solo (or with a spouse) and want to save the most the tax code allows.
2. SEP IRA: best for the least paperwork
A SEP IRA is a single employer contribution — there's no employee deferral piece to manage. You, as the employer, contribute a flat percentage of compensation, capped at 25% of compensation or, for a sole proprietor or partner, roughly 20% of net self-employment income after the self-employment tax deduction. Setup is one form at most brokerages, and there's nothing to file annually with the IRS.
SEP IRA pros:
- No annual IRS filing, regardless of account balance
- Can be opened and funded as late as your extended tax filing deadline (October 15) for the prior year
- Contribution percentage can flex year to year based on how the business performed
SEP IRA cons:
- No catch-up contribution for savers 50 and older
- No loan provision and no Roth option at most custodians
- If you have eligible employees, you generally must contribute the same percentage of pay for them that you take for yourself
Best for: owners who want to open, fund, and forget a plan with zero ongoing filings, including those comfortable covering a small employee headcount at the same contribution rate.
SEP IRA verdict: Buy if simplicity matters more to you than squeezing out every dollar of contribution room.
3. SIMPLE IRA: best for owners with employees who want a lower-cost plan
A SIMPLE IRA fits a different problem than the first two — it's built for a business that already has employees and wants a plan cheaper to run than a full 401k. You commit to either matching employee deferrals or making a fixed contribution for everyone eligible, and setup and recordkeeping stay lighter than a 401k.
SIMPLE IRA pros:
- Lower administrative cost than a Solo 401k or standard 401k
- Employees can defer their own pay in addition to your contribution
- Straightforward to establish through most payroll providers and brokerages
SIMPLE IRA cons:
- Lower elective deferral ceiling than a 401k
- Withdrawals or rollovers within the first two years of participation carry a steeper early withdrawal penalty than other IRAs
- Once you commit to the employer contribution formula for the year, you're locked into it
Best for: owners with W-2 employees who want a mandatory-but-capped employer contribution instead of a discretionary profit-sharing formula.
SIMPLE IRA verdict: Hold — worth a look once you have employees; skip it if you're still a one-person operation.
How we ranked these
The order above follows the criteria a self-employed owner actually weighs first: contribution ceiling, paperwork, employee rules, catch-up access, loan and Roth availability, and deadline flexibility. A Solo 401k wins on ceiling and flexibility for a one-person business, a SEP IRA wins on simplicity, and a SIMPLE IRA wins once payroll includes other people. Before you sign paperwork with any custodian, 8 questions to ask a financial advisor is worth running through so you're not evaluating the plan in isolation from the rest of your finances.
Model Your Options With Dillon
A fee-only fiduciary review of SEP IRA, Solo 401k, and SIMPLE IRA fit for your actual net income.
Which plan should you choose?
If you're still deciding between a SEP IRA and a Solo 401k in 2026, use headcount as the tiebreaker first. No employees and you want to save the most: choose a Solo 401k. A few employees, or you just want to sign one form and move on: choose a SEP IRA. Employees who should share in a retirement benefit: choose a SIMPLE IRA. Run the numbers against your actual net income before you commit — is investment management worth it for a small business owner walks through when paying for that kind of planning pays for itself.
FAQ
What's the difference between a SEP IRA and a Solo 401k?
A SEP IRA is a single employer contribution based on a percentage of compensation, while a Solo 401k lets you contribute as both employee and employer, which usually allows a higher total contribution at the same income level. The Solo 401k also offers catch-up contributions and a loan option that a SEP IRA does not.
Can I contribute to both a SEP IRA and a Solo 401k in the same year?
You generally can't fund both for the same self-employment income in the same year without running into overlapping contribution limits, since both draw from the same overall annual cap. Most owners pick one plan for a given business and stick with it.
Is a Solo 401k better than a SEP IRA for a single-owner LLC?
For a single-owner LLC with no employees, a Solo 401k usually allows a higher total contribution because it stacks an employee deferral on top of the employer contribution. It also adds catch-up eligibility for owners 50 and older, which a SEP IRA doesn't offer.
Do I need an EIN to open either plan?
Most custodians require an Employer Identification Number to open a Solo 401k or a SEP IRA, even for a sole proprietor with no employees. A Social Security number alone typically isn't accepted for the plan application.
Can I take a loan from a SEP IRA?
No. A SEP IRA does not permit loans; only a Solo 401k (or standard 401k) can include a loan provision. Taking money out of a SEP IRA before retirement age counts as a distribution and may trigger tax and penalty.
What happens to my Solo 401k if I hire employees later?
Bringing on a full-time common-law employee generally means the plan has to extend coverage to them, which turns a Solo 401k into a standard employer 401k with added compliance requirements. Many owners switch to a SEP IRA or SIMPLE IRA at that point instead.
How much does it cost to set up a Solo 401k in 2026?
Setup cost depends on the custodian and whether you use a prototype plan document or a custom one; check current pricing directly with the provider you're considering. The bigger cost driver over time is the Form 5500-EZ filing once plan assets pass $250,000.
Which plan lets me contribute the most as a sole proprietor?
A Solo 401k typically allows the highest total contribution for a sole proprietor with no employees, because it combines an employee deferral with an employer profit-sharing contribution. Confirm current-year dollar limits on IRS.gov before you fund either account, since they're indexed annually.
One last thing
The deadline gap surprises most owners: a SEP IRA can be opened and funded as late as your extended tax filing deadline of October 15, but the salary deferral portion of a Solo 401k generally has to be elected by December 31 of the same year. If you're deciding late in the year and haven't set up a Solo 401k yet, you may have already missed the deferral window for that tax year even though a SEP IRA is still on the table.
