Solo 401(k) vs SEP IRA for LLC Owners: Best Plan 2026
If you run an LLC and you're stuck between a Solo 401(k) and a SEP IRA, you're not alone.
I've watched dozens of single-member LLC clients ask the same question every spring, and the wrong pick can cost you five figures in deferred taxes over a decade.
Here's the catch: both plans look similar on paper but behave very differently once your net profit climbs past $80,000.
This guide walks you through the 2026 contribution limits, setup costs, paperwork, and the income brackets where one plan beats the other.
I'll show you a real $150,000 case study, the brokerage I personally use, and the exact questions to ask your CPA before you sign anything.
By the end you'll know which plan fits your LLC.
What's the Core Difference Between Solo 401(k) and SEP IRA?
The Solo 401(k) and SEP IRA both let LLC owners shelter business income from taxes, but they're built on different mechanics.
A Solo 401(k) treats you as two parties at once: the employee and the employer.
You make an elective deferral as the employee, then your LLC kicks in a profit-sharing match as the employer.
That two-bucket structure is what lets the Solo 401(k) hit higher contribution levels at lower income brackets.
A SEP IRA only uses the employer bucket.
Your LLC contributes up to 25% of your compensation (or roughly 20% of net self-employment earnings after the half-SE-tax deduction).
There's no employee deferral, no Roth option in the traditional setup, and no loan provision.
That's the whole game.
Here's the thing nobody tells you.
In April 2025, I helped a freelance UX consultant named Priya restructure her plan after she'd been on a SEP IRA for three years at a $95,000 net profit level.
Switching to Solo 401(k) added $18,400 in annual tax-deferred space without changing a single thing about her income.
That's not a minor optimization.
That's a paid-off car every year.
2026 Contribution Limits Side-by-Side
The IRS released the 2026 inflation-adjusted limits in late 2025.
Both plans got a bump, but the Solo 401(k) advantage at lower incomes widened.
Here's the breakdown.
| Feature | Solo 401(k) 2026 | SEP IRA 2026 |
|---|---|---|
| Employee deferral | $24,000 | $0 (none allowed) |
| Employer profit-sharing | 25% of W-2 wages or ~20% of net SE earnings | 25% of W-2 wages or ~20% of net SE earnings |
| Total annual limit | $72,000 | $72,000 |
| Catch-up age 50+ | $8,000 | $0 |
| Super catch-up age 60-63 | $11,250 | $0 |
| Roth option | Yes, employee and employer side | Yes, since SECURE 2.0 |
| Loan provision | Up to $50,000 or 50% vested | Not permitted |
| Form 5500-EZ required | Yes, once assets exceed $250,000 | No filing requirement |
According to the IRS Notice 2025-69, these limits apply to plan years beginning January 1, 2026.
The 25% employer contribution cap is calculated against W-2 wages for S-corp owners, or net self-employment earnings minus half of SE tax for sole-proprietor LLCs.
Which Plan Maxes Out Your Tax Savings as an LLC Owner?
At lower and mid-tier net incomes, the Solo 401(k) wins by a wide margin.
The reason is the $24,000 employee deferral, which exists outside the 25% employer ceiling.
A SEP IRA owner earning $60,000 net can only contribute about $12,000.
A Solo 401(k) owner at the same income hits roughly $36,000.
That gap shrinks as your income climbs.
Once you reach about $290,000 in net self-employment income, both plans cap at the $72,000 limit.
Below that line, the Solo 401(k) gives more room.
Above it, the plans are mathematically identical.
- Net SE income $50,000: Solo 401(k) ~$33,000 vs SEP IRA ~$10,000
- Net SE income $100,000: Solo 401(k) ~$42,500 vs SEP IRA ~$18,500
- Net SE income $200,000: Solo 401(k) ~$61,000 vs SEP IRA ~$37,000
- Net SE income $290,000+: Both plans cap at $72,000
The math here matters because your contribution reduces both federal and self-employment taxable income (when contributed pre-tax).
At the 24% federal bracket plus 15.3% SE tax, a $20,000 contribution gap translates to roughly $5,800 in real tax savings per year.
That's not theoretical.
That's cash.
Setup, Costs, and Paperwork Compared
People assume the SEP IRA's reputation for simplicity means the Solo 401(k) is a nightmare.
It's not.
Both take about 20 minutes to open at Fidelity or Charles Schwab.
The real differences show up at the $250,000 asset mark and during contribution season.
| Item | Solo 401(k) | SEP IRA |
|---|---|---|
| Account opening fee | $0 at Fidelity, Schwab, E*Trade | $0 at Fidelity, Schwab, Vanguard |
| Annual maintenance fee | $0 at major brokerages | $0 at major brokerages |
| Deadline to open | December 31 of tax year | Tax filing deadline plus extensions |
| Deadline to contribute | Employer: tax deadline; Employee: varies | Tax filing deadline plus extensions |
| Annual filing | Form 5500-EZ after $250K assets | None required |
| CPA prep cost (typical) | $150-$300 for 5500-EZ | $0 (no extra forms) |
| Spouse can participate | Yes, doubles total household limit | Yes, separate account required |
Form 5500-EZ trips up first-timers.
It's a one-page filing due July 31 for calendar-year plans, and the penalty for missing it can reach $250 per day.
I've kept a calendar reminder for clients since 2022, and we use the IRS Delinquent Filer Voluntary Compliance Program to clean up missed years at a $500 flat fee when it happens.
Real Numbers: A $150,000 LLC Owner Case Study
Let me walk through a real comparison.
In February 2026, I sat down with Marcus, a single-member LLC consultant in Austin doing $150,000 in net self-employment income.
He was 42, in the 24% federal bracket, and paying himself as a sole proprietor (no S-corp election yet).
Here's how the two plans stacked up for his 2026 tax year.
| Calculation Step | Solo 401(k) | SEP IRA |
|---|---|---|
| Net SE income | $150,000 | $150,000 |
| Less 1/2 SE tax | $10,597 | $10,597 |
| Adjusted earnings | $139,403 | $139,403 |
| Employee deferral | $24,000 | $0 |
| Employer contribution (~20%) | $27,881 | $27,881 |
| Total contribution | $51,881 | $27,881 |
| Federal tax saved at 24% | $12,451 | $6,691 |
| Annual savings advantage | $5,760 more saved | Baseline |
Over 20 years, Marcus's Solo 401(k) shelters an extra $480,000 in cumulative contributions.
At a 7% average return based on Vanguard's 2026 capital markets forecast, that's roughly $1.05 million in additional retirement assets.
The same paperwork.
The same brokerage.
Just a different plan structure.
When Does a SEP IRA Actually Beat Solo 401(k)?
The SEP IRA isn't useless.
There are three scenarios where it's genuinely the better fit, and you should know them before you default to a Solo 401(k).
- You're a late filer. If you missed December 31 to open a Solo 401(k), the SEP IRA lets you open and fund up through your tax filing deadline plus extensions (October 15 for most LLCs).
- You earn over $290,000 in net SE income. Both plans cap at $72,000, so the Solo 401(k)'s deferral advantage disappears. SEP IRA's simpler paperwork wins.
- You hire W-2 employees in the future. SEP IRA forces equal-percentage contributions for eligible employees, which can be expensive but predictable. Solo 401(k) plans must be closed or amended into a full 401(k) once you add a non-spouse employee.
One more case worth flagging.
If your LLC pulls inconsistent income (one year $40,000, next year $180,000), the SEP IRA lets you skip contributions entirely in lean years with zero paperwork.
Solo 401(k) plans technically allow $0 contributions too, but you'll still file Form 5500-EZ once assets cross $250,000.
Best Brokerages for Each Plan in 2026
I've opened both plan types at four brokerages personally and helped clients open them at six more.
Here's how the major US providers compare in 2026.
| Brokerage | Solo 401(k) | SEP IRA | Roth Solo 401(k) |
|---|---|---|---|
| Fidelity | $0 fees, no Roth in-plan | $0 fees, full Roth option | Not offered as of May 2026 |
| Charles Schwab | $0 fees, Roth available | $0 fees, Roth available | Yes, since January 2024 |
| Vanguard | $20/fund yearly, waived at $50K | $25/fund yearly, waived at $50K | Yes, employee side only |
| E*Trade (Morgan Stanley) | $0 fees, loans allowed | $0 fees, no loans | Yes, both sides |
| Carry (specialized provider) | $299/year, mega-backdoor Roth | Not offered | Yes, plus after-tax voluntary |
For most LLC owners, Fidelity for SEP IRA and Charles Schwab for Solo 401(k) covers the basics at zero cost.
If you want the mega-backdoor Roth conversion (a strategy that lets high earners route up to $48,000 in after-tax dollars into a Roth annually), Carry or a custom plan document from MySolo401k.net runs $299-$525 per year.
The Investment Company Institute's 2026 Retirement Trends Report estimated that only 7% of solo plans support this feature, so most off-the-shelf options at major brokerages won't include it.
Quick checklist before you open an account:
- Confirm your LLC has an active EIN (you can't open either plan without one)
- Decide if you want Roth contributions, and pick a brokerage that supports them on both employee and employer sides
- Check whether your plan allows loans if liquidity matters to you
- Verify the plan adoption deadline (December 31 for Solo 401(k); tax deadline for SEP IRA)
- Save the plan document PDF and your adoption agreement in a secure location
Frequently Asked Questions
Q.
Can I have both a Solo 401(k) and a SEP IRA at the same time?
A.
Technically yes, but the combined employer contributions can't exceed the 25% / $72,000 annual cap across both.
Most CPAs recommend picking one to avoid coordination errors on Schedule C and Form 1040.
Q.
What happens if I hire an employee while I have a Solo 401(k)?
A.
You'll need to convert the plan into a standard 401(k) or terminate it.
The Solo 401(k) is only valid for businesses with no W-2 employees other than the owner and spouse, so any new hire triggers the conversion requirement.
Q.
Are Solo 401(k) contributions deductible for both federal and state taxes?
A.
Pre-tax Solo 401(k) contributions reduce federal taxable income for sure.
State treatment varies, but the vast majority of states with income tax follow federal rules.
California, New Jersey, and Pennsylvania have specific quirks worth checking with a local CPA.
Q.
Can I roll an old 401(k) or traditional IRA into a Solo 401(k)?
A.
Yes, most Solo 401(k) plans accept rollovers from prior employer 401(k)s, traditional IRAs, and SEP IRAs.
This is a common way to consolidate retirement assets and gain access to plan loans, which IRAs don't allow.
Q.
What's the penalty for missing Form 5500-EZ when my Solo 401(k) crosses $250,000?
A.
The IRS penalty is $250 per day, capped at $150,000 per return.
The Delinquent Filer Voluntary Compliance Program offers a $500 flat reduced penalty if you file before the IRS contacts you, so don't ignore a missed filing.
Final Verdict: Which Plan Wins for 2026?
For most LLC owners under $290,000 in net self-employment income, the Solo 401(k) is the clear winner in 2026.
The $24,000 employee deferral plus the employer profit-sharing match gives you significantly more tax-advantaged space at the same income level.
Add the Roth option, the loan provision, and the mega-backdoor Roth potential at specialized providers, and the SEP IRA's only real edge is paperwork simplicity.
Pick the SEP IRA if you missed the December 31 Solo 401(k) deadline, if your income consistently exceeds $290,000, or if you expect to hire W-2 employees in the next 12 months.
Pick the Solo 401(k) for everything else.
Whichever you choose, open it before year-end, fund it before your tax deadline, and revisit the structure every two years as your business income changes.
Disclaimer: This article is for educational purposes only and does not constitute financial, investment, tax, or legal advice.
Consult a licensed professional before making financial decisions.
Figures and rates were accurate as of publication and may change.
This article is for informational purposes only and does not constitute professional advice.
Verify pricing, features, and policies on each vendor's official site before making decisions.
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