If you run a one-person business, choosing between a Solo 401(k) and a SEP-IRA is one of the highest-leverage financial decisions you can make. Both plans let self-employed individuals build tax-advantaged retirement savings far beyond what a standard IRA allows, but they work very differently once you run the numbers.
I’ve worked with hundreds of self-employed clients over the years, and the same question always comes up: “Which plan gives me the most for my situation?” The honest answer depends on your income, your age, your willingness to handle paperwork, and whether you plan to hire anyone in the next few years.
In this guide, I’ll walk you through how each plan actually works in 2026, how the contribution limits compare side by side, and which plan makes sense for which type of one-person business. I’ll also show you the SECURE 2.0 changes that just took effect, because they shift the math for many readers.
Table of Contents
What Is a Solo 401(k)?
A Solo 401(k) — also called an individual 401(k) or one-participant 401(k) — is a retirement plan designed specifically for business owners with no full-time employees other than a spouse. It lets you contribute as both employee and employer, which is the source of its main advantage.
As the employee, you can defer up to $24,500 of your compensation in 2026 through salary deferrals. As the employer, you can contribute an additional amount tied to your net self-employment income or W-2 wages. Combined, the two contributions can reach $72,000 or more depending on your age and income.
To qualify, you must operate a trade or business as a sole proprietor, single-member LLC, partnership, or corporation. The critical rule is that you cannot have any full-time employees other than your spouse. Part-time workers under 1,000 hours per year are excluded from this rule, which gives you some flexibility as you grow.
You can choose between a traditional Solo 401(k) with pre-tax contributions or a Roth Solo 401(k) with after-tax contributions. Many providers let you split contributions between both buckets, which gives you tax diversification in retirement.
What Is a SEP-IRA?
A SEP-IRA (Simplified Employee Pension IRA) is an IRA-based retirement plan funded entirely by employer contributions. For a one-person business, you are both the employer and the employee, but only the employer side gets to contribute.
The contribution limit is up to 25% of your net self-employment earnings, capped at $72,000 in 2026. If you’re an S-Corp owner, the limit applies to your W-2 wages rather than pass-through profit.
Setting up a SEP-IRA is genuinely simple. Most major brokerages let you open one in under 15 minutes, and the IRS Form 5305-SEP serves as the plan document. There’s no annual filing requirement unless your plan assets exceed $250,000.
Until SECURE 2.0, SEP-IRAs only supported traditional (pre-tax) contributions. Starting in 2026, you can now elect Roth treatment for SEP contributions, though the IRS guidance is being finalized for some edge cases. For most people reading this in 2026, the practical answer is still that SEP-IRAs function as pre-tax accounts.
Solo 401(k) vs SEP-IRA: Key Differences at a Glance (2026)
The fastest way to see where these plans diverge is to compare them feature by feature. Here’s the table I built after comparing the two plans across every dimension that matters to a self-employed person.
| Feature | Solo 401(k) | SEP-IRA |
|---|---|---|
| Contribution types | Employee deferrals + employer profit sharing | Employer contributions only |
| 2026 employee deferral limit | $24,500 (plus catch-up) | Not available |
| 2026 employer contribution limit | Up to 25% of compensation | Up to 25% of compensation |
| 2026 total contribution limit | $72,000 (under 50), $80,000+ with catch-up | $72,000 maximum |
| Catch-up contributions (age 50+) | Yes — $8,000 employee deferral | No catch-up contributions allowed |
| Enhanced catch-up (ages 60-63) | Yes — $11,250 in 2026 | Not available |
| Roth option | Yes (both employee and employer) | Limited (Roth SEP available under SECURE 2.0) |
| Participant loans | Yes — up to $50,000 or 50% of balance | No |
| Voluntary after-tax contributions | Yes (enables mega backdoor Roth) | No |
| Setup complexity | Moderate — requires plan document | Low — usually a brokerage form |
| Annual filing (Form 5500-EZ) | Required if assets exceed $250,000 | Not required |
| Spouse working in business | Spouse can have separate account | Spouse treated as employee |
| Works for S-Corps | Yes — based on W-2 wages | Yes — based on W-2 wages |
| Nondiscrimination testing | Exempt (one-participant only) | Exempt (one-participant only) |
Look at row three. That single row is why most one-person businesses end up choosing a Solo 401(k) over a SEP-IRA. The employee deferral gives you an extra $24,500 of contribution room that the SEP-IRA simply can’t match.
2026 Contribution Limits for Solo 401(k) and SEP-IRA
Numbers change every year, so let me lay out exactly what you can put into each plan in 2026. I’ll separate the limits into the two main contribution types so you can see where the Solo 401(k) advantage comes from.
Employee Elective Deferrals (Solo 401(k) only)
The employee side of a Solo 401(k) works just like a traditional employer 401(k). You can defer up to $24,500 of your compensation in 2026, pre-tax or Roth.
If you’re 50 or older, you can add a $8,000 catch-up contribution, bringing your employee-side total to $32,500. SECURE 2.0 also created an enhanced catch-up for people aged 60 to 63 — they can contribute $11,250 in 2026 instead of the standard $8,000.
This employee contribution is the single biggest advantage of the Solo 401(k). A SEP-IRA has no equivalent feature.
Employer Contributions (Both Plans)
As the employer, both plans let you contribute up to 25% of your compensation. For sole proprietors and single-member LLCs, the calculation uses net self-employment earnings minus the deductible portion of self-employment tax.
For practical purposes, the effective contribution rate works out to roughly 20% of net self-employment income for sole proprietors. S-Corp owners calculate the 25% directly against W-2 wages.
For 2026, the 415(c) annual addition limit caps total employer-side contributions at $72,000 per participant.
Putting Both Sides Together
When you stack the employee deferral on top of the employer contribution, here’s the math:
Under age 50: $24,500 + employer contribution up to $72,000 = up to $72,000 total (employer contribution is reduced if needed to stay under the cap)
Age 50-59: Add $8,000 catch-up to total potential
Ages 60-63: Add $11,250 enhanced catch-up
Age 64+: Standard $8,000 catch-up
The internal rule is called the 415(c) annual addition limit, and it controls how much can go into the account from all sources combined. The employee deferral counts against it, the employer contribution counts against it, and after-tax contributions count against it.
Why the Solo 401(k) Often Wins for One-Person Businesses
Most of the self-employed clients I work with end up choosing a Solo 401(k) once they see the contribution math. Here’s why.
Higher Contributions at Moderate Income
The Solo 401(k) advantage is biggest when your net self-employment income falls between roughly $50,000 and $200,000. At these income levels, the employee deferral adds a meaningful boost on top of the employer contribution that both plans offer.
Take someone earning $100,000 in net self-employment income. A SEP-IRA lets them contribute about $18,587 (20% effective rate). A Solo 401(k) lets them contribute $24,500 as employee deferral plus $18,587 as employer — totaling $43,087. That’s more than double.
At very high incomes (over $350,000), the two plans converge because the $72,000 415(c) cap binds both of them.
Catch-Up Contributions After Age 50
If you’re 50 or older, the Solo 401(k) catch-up contribution is unavailable in a SEP-IRA at all. The IRS allows catch-ups only in 401(k)-style plans, not in IRAs. So if you’re a 52-year-old consultant, the Solo 401(k) is the only way to get that extra $8,000 (or $11,250 if you’re 60-63).
Roth Contributions
A Solo 401(k) has supported designated Roth contributions for years. You can elect to put some or all of your employee deferrals into a Roth bucket, where qualified withdrawals in retirement are tax-free.
For high earners who can’t make direct Roth IRA contributions, the Solo 401(k) provides a clean path to Roth savings. This is one of the few ways a high-income self-employed person can build tax-free retirement income.
Participant Loans
Solo 401(k)s allow participant loans of up to $50,000 or 50% of your vested account balance, whichever is less. You pay yourself back with interest at a rate you set within IRS guidelines.
This feature is genuinely useful for self-employed people who need access to capital but don’t want to permanently deplete their retirement savings. Real estate investors, business owners considering expansion, and anyone with irregular income tend to value this feature most.
Voluntary After-Tax Contributions and the Mega Backdoor Roth
Many Solo 401(k) plans allow voluntary after-tax contributions beyond the regular limits. Combined with in-service rollovers to a Roth IRA, this enables the mega backdoor Roth strategy.
In 2026, you can contribute up to roughly $70,000+ in after-tax money into your Solo 401(k) depending on your age and income, then convert it to a Roth IRA. This is a powerful tax-planning move that a SEP-IRA cannot support.
When a SEP-IRA Makes More Sense
Not everyone should choose a Solo 401(k). Here are the situations where a SEP-IRA is the better fit.
Administrative Simplicity
If your time is limited or you simply don’t want to deal with retirement plan paperwork, a SEP-IRA is dramatically easier. There’s no plan document to maintain, no annual discrimination testing concerns, and no Form 5500-EZ filing until assets exceed $250,000.
Many brokerages let you open a SEP-IRA online in 10-15 minutes. Setting up a Solo 401(k) typically requires selecting a provider, signing a plan document, and choosing an effective date.
Lower or Highly Variable Income
The SEP-IRA’s employer-only contribution is optional each year. If you have a down year, you can skip the contribution without losing the plan. A Solo 401(k) is also flexible about employer contributions, but you may still want to keep the plan active for the employee deferral feature.
For freelancers and gig workers whose income swings year to year, the SEP-IRA’s pure employer contribution model can be a feature, not a bug.
Income Under $30,000
If your net self-employment income is below roughly $30,000, both plans produce very similar contribution room. The SEP-IRA may actually beat a Solo 401(k) once you factor in setup complexity, because the extra employee deferral won’t add much to the total.
At this income level, you should also consider whether a Roth IRA makes sense. Direct Roth IRA contributions phase out at higher incomes but are fully available at lower ones.
SECURE 2.0 Changes That Affect Both Plans in 2026
SECURE 2.0 was signed into law in late 2022, and its provisions continue to roll out year by year. Here are the changes that actually affect a Solo 401(k) vs SEP-IRA decision in 2026.
Enhanced Catch-Up for Ages 60 to 63
The enhanced catch-up contribution for participants aged 60 to 63 became effective for plan years beginning after December 31, 2024. For 2026, this means anyone aged 60-63 can contribute $11,250 as their employee catch-up in a Solo 401(k), instead of the standard $8,000 catch-up.
This applies only to 401(k)-style plans. SEP-IRAs do not offer catch-up contributions at all, so the Solo 401(k) advantage grows even larger for older self-employed individuals.
Roth Catch-Up Requirement for High Earners
Starting in 2026, employees with FICA wages exceeding $150,000 in the prior year must make catch-up contributions on a Roth (after-tax) basis. This applies to 401(k), 403(b), and governmental 457(b) plans.
If you’re a high-earning S-Corp owner paying yourself a large W-2, your Solo 401(k) catch-up contributions will need to be Roth in 2026. This doesn’t reduce your contribution room — it just changes the tax treatment. Most providers have updated their systems to handle this automatically.
Note: This requirement does not currently apply to SEP-IRAs because they don’t offer catch-up contributions.
Roth SEP Contributions
SECURE 2.0 allowed employers to offer Roth treatment for SEP contributions, beginning in 2026. In practice, most SEP providers haven’t fully implemented this option yet, but it’s worth asking your custodian if it’s available.
Required Minimum Distributions (RMDs)
The RMD age for both plans is now 73 in 2026, rising to 75 in 2033. This gives most one-person business owners a bit more time before mandatory distributions kick in.
Real-World Contribution Scenarios
Numbers tell the story better than theory. Here are three realistic scenarios showing how the two plans compare.
Scenario 1: Sole Proprietor Earning $80,000 Net
A freelance graphic designer reports $80,000 of net self-employment income on Schedule C. Their self-employment tax is about $10,734, of which half ($5,367) is deductible.
SEP-IRA contribution: 20% × ($80,000 − $5,367) = $14,927
Solo 401(k) contribution: $24,500 employee deferral + 20% × ($80,000 − $5,367 − $24,500) employer = $24,500 + $10,027 = $34,527
The Solo 401(k) wins by roughly $19,600 in tax-deductible retirement contributions.
Scenario 2: S-Corp Owner Taking $150,000 W-2
An S-Corp owner pays herself $150,000 in W-2 wages and takes the rest of the profit as distributions. She is under 50.
SEP-IRA contribution: 25% × $150,000 = $37,500
Solo 401(k) contribution: $24,500 employee + 25% × $150,000 = $24,500 + $37,500 = $62,000 (under the $72,000 cap)
The Solo 401(k) wins by $24,500 — exactly the employee deferral limit.
Scenario 3: Consultant at $300,000 Net Income
A management consultant reports $300,000 net self-employment income and is 55 years old.
SEP-IRA contribution: Capped at $72,000 (the 415(c) annual addition limit)
Solo 401(k) contribution: $24,500 + $8,000 catch-up + employer contribution up to $72,000 cap = around $72,000 total (the cap binds both plans at this income level)
At very high incomes, the plans converge. The Solo 401(k) still wins because of the catch-up contribution, but the gap closes significantly.
What Happens If You Hire Employees?
The Solo 401(k) only works if you truly have a one-person business. The moment you hire a full-time non-spouse employee, the rules change.
Solo 401(k) Becomes a Regular 401(k)
Your Solo 401(k) automatically converts to a multi-participant 401(k) the day you have an eligible employee. You’ll need to include them in the plan, run nondiscrimination testing, and meet additional IRS requirements.
Many providers who only offer Solo 401(k) plans will not support you through this transition. You’ll either need to find a new provider or move to a different plan type entirely.
SEP-IRA Includes Eligible Employees
A SEP-IRA must cover all employees who meet the eligibility requirements (typically age 21 and at least 1,000 hours in the prior year). You must contribute the same percentage of compensation for each eligible employee.
This is one reason SEP-IRAs are popular for businesses with occasional or part-time help — you can structure eligibility to exclude most workers.
Planning Ahead
If you think you’ll hire even one full-time employee within the next few years, talk to a retirement plan advisor before choosing your plan. The wrong choice can force an expensive transition.
Can You Contribute to Both Plans in the Same Year?
Yes, you can maintain both a Solo 401(k) and a SEP-IRA in the same year, but with a critical caveat: total contributions across both plans are subject to the same $72,000 415(c) annual addition limit.
You can’t double-dip and contribute $144,000. The combined employer-side contributions and any employee deferrals share the single $72,000 cap.
This strategy is most useful when your spouse works in the business. A spouse-employee can have their own Solo 401(k) account, and you as the employer can make employer contributions on their behalf — effectively doubling household contribution capacity.
Steps to Open Each Account
Opening a Solo 401(k)
Choose a provider that offers Solo 401(k) plans (Fidelity, Schwab, Vanguard, E*TRADE, or specialty providers like Guideline and Ubiquity).
Adopt a written plan document with an effective date no later than your business tax filing deadline, including extensions.
Get an EIN if you don’t already have one.
Open a trust or custodial account at your chosen investment provider.
Begin making employee deferrals through payroll or self-employed accounting.
Opening a SEP-IRA
Choose a brokerage or mutual fund company.
Complete IRS Form 5305-SEP (or the provider’s equivalent online form).
Provide each eligible employee with the required disclosures.
Make employer contributions by your tax filing deadline, including extensions.
FAQs
Why is a Solo 401(k) better than a SEP-IRA?
A Solo 401(k) is usually better than a SEP-IRA for a one-person business because it lets you contribute as both employee and employer. The employee deferral of up to $24,500 in 2026 (plus catch-up contributions) gives you more contribution room than the SEP-IRA’s employer-only structure. The Solo 401(k) also offers participant loans, Roth contributions, and voluntary after-tax contributions that a SEP-IRA cannot match.
How much can a self-employed person contribute to a SEP-IRA in 2026?
In 2026, a self-employed person can contribute up to 25% of net self-employment earnings to a SEP-IRA, with a maximum dollar limit of $72,000 in 2026. For sole proprietors, the effective contribution rate works out to roughly 20% of net self-employment income after deducting half of self-employment tax. SEP-IRAs do not allow catch-up contributions, even for participants age 50 and older.
What is the downside of a Solo 401(k)?
The main downsides of a Solo 401(k) are administrative complexity, occasional paperwork requirements, and the need to formally close the plan if you stop being self-employed. You may also need to file Form 5500-EZ once plan assets exceed $250,000, and you’ll need to maintain a written plan document. Some providers charge setup or annual fees, though many major brokerages offer free Solo 401(k) plans.
Can I have both a SEP and a Solo 401(k) in the same year?
Yes, you can maintain both a SEP-IRA and a Solo 401(k) in the same year, but combined contributions across both plans are subject to the same $72,000 415(c) annual addition limit for 2026. You cannot contribute $72,000 to each plan. This strategy is most useful when your spouse also works in the business, allowing your household to potentially contribute more than a single business could.
The Bottom Line on Solo 401(k) vs SEP-IRA
For most one-person businesses, the Solo 401(k) is the stronger choice in 2026. The employee deferral, catch-up contributions, Roth option, participant loans, and mega backdoor Roth potential all favor the Solo 401(k).
Choose a SEP-IRA if your income is under $30,000, your income varies dramatically year to year, or you want to minimize plan administration.
Whatever you decide, run your specific numbers with a CPA or qualified retirement plan advisor before opening the account. Contribution limit calculations for self-employed individuals are unforgiving, and a small mistake can trigger excess contribution penalties.
Take 30 minutes this week to map out your projected income, your age, and your retirement savings goal. Then pick the plan that fits — and start contributing before the year slips away.