SEP-IRA vs Solo 401(k): Which Retirement Account Wins for the Self-Employed Investor

TL;DR: At $200,000 net self-employment income in 2026, a Solo 401(k) lets you contribute $61,674 versus $37,174 in a SEP-IRA, a $24,500 advantage that comes entirely from the Solo 401(k)'s employee deferral feature. According to IRS Notice 2025-67, both accounts share a $72,000 Section 415 cap for 2026, but the Solo 401(k) lets you reach that ceiling at significantly lower income. The SEP-IRA's advantages are real too: zero administration, a late setup deadline, and one of the cleanest account structures available. Choosing between them depends on your income level, your tolerance for paperwork, and whether you plan to invest in leveraged real estate inside a retirement account.

2026 Contribution Limits: The Exact IRS Numbers

Per IRS Notice 2025-67, here are the official 2026 figures for both account types.

SEP-IRA 2026:

• Maximum contribution: $72,000 (lesser of 25% of compensation or $72,000)
• Compensation cap: $360,000
• Catch-up contributions: None available
• Roth option: Available at some custodians under SECURE 2.0, but verify with yours before assuming

Solo 401(k) 2026:

• Employee elective deferral: $24,500
• Employer profit-sharing: up to approximately 18.587% of net self-employment income
• Combined maximum (Section 415 cap): $72,000
• Catch-up (age 50 to 59 and 64+): $8,000 additional
• Super catch-up (age 60 to 63): $11,250 additional
• Roth employee deferrals: Available

The structural difference: a SEP-IRA only allows employer-side contributions. A Solo 401(k) lets you wear two hats, contributing as both employee and employer. That employee deferral of $24,500 is what creates the gap at every income level below the Section 415 ceiling.

One number that trips up even experienced advisors: the effective employer contribution rate for self-employed individuals is approximately 18.587% of net Schedule C profit, not 25% of gross income. The IRS calculation requires you to first deduct half of your self-employment tax, then solve a circular equation where the contribution itself reduces the income base. Use the worksheet in IRS Publication 560 to get the exact figure for your situation.

The Math at $100K, $200K, and $300K

The table below uses 2026 limits and assumes a sole proprietor with no W-2 income from another employer, no employees, and standard self-employment tax deduction calculations.

Net Schedule C Income	SEP-IRA Contribution	Solo 401(k) Total	Solo 401(k) Advantage	Solo 401(k) Multiplier
$100,000	$18,587	$43,087	+$24,500	2.32x
$200,000	$37,174	$61,674	+$24,500	1.66x
$300,000	$55,765	$72,000	+$16,235	1.29x

At $100,000, the Solo 401(k) delivers more than twice the tax-deferred capacity. The employer contribution to both plans is identical at approximately $18,587. The Solo 401(k) stacks the $24,500 employee deferral directly on top of that figure.

At $200,000, the advantage stays constant at $24,500. The employer contributions are again equal ($37,174 each). The employee deferral is the only variable that separates the two accounts.

At $300,000, the Solo 401(k) hits the $72,000 Section 415 ceiling first. The employer contribution alone reaches approximately $55,765, so only a partial employee deferral of $16,235 fits before hitting the cap. The SEP-IRA reaches $55,765 total. The Solo 401(k) still wins, but the margin narrows.

To max the SEP-IRA at its $72,000 ceiling, you need net self-employment income of approximately $360,000. At that level, both plans share the same cap and neither can exceed it.

If you have a W-2 job: The $24,500 employee deferral is a per-person aggregate across all 401(k) plans. If you already defer $24,500 into your employer's 401(k), you cannot add another $24,500 to a Solo 401(k) for the same year. Account for this before projecting your total retirement savings.

Admin Complexity: Zero Versus Occasional Headache

The SEP-IRA wins on simplicity. There is no plan document, no annual filing, and no deadlines beyond the contribution deadline. You open the account at any brokerage, make your contribution, take the deduction. That is the complete administrative burden for the life of the account.

The Solo 401(k) requires more work. You need an adoption agreement and plan document at setup. Most custodians provide a prototype document, so this is a one-time task, not ongoing complexity. The more significant obligation arrives once your total plan assets exceed $250,000 at the end of any plan year: you must file Form 5500-EZ annually with the IRS. The deadline is July 31, extended to October 15 on request. Failure to file carries a $250-per-day penalty capped at $150,000.

If you miss the filing, the Delinquent Filer Voluntary Compliance Program (DFVCP) lets you self-report and cap penalties at $500 per return, with a maximum of $1,500 per plan. That outcome is far better than the statutory penalty, but the goal is simply filing on time.

One practical trap: Fidelity, Schwab, and the Ascensus platform that now holds the old Vanguard Solo 401(k) business do not file Form 5500-EZ on your behalf. The obligation falls entirely on you as plan sponsor. If your Solo 401(k) assets cross $250,000, put July 31 on your calendar every year.

Self-Directed Options: Custodians That Allow Alternatives

If you want to invest in private equity, real estate, promissory notes, or other alternatives inside a retirement account, your custodian choice determines what is possible. The major discount brokerages limit both their SEP-IRA and Solo 401(k) products to publicly traded securities. For alternatives, these three platforms are most commonly used.

Equity Trust Company is one of the oldest self-directed custodians. It supports both self-directed IRA (including SEP-IRA) and Solo 401(k). Setup fee: $1,295 one-time. Annual fee: $695. At $500,000 in assets, that annual fee represents a 0.14% effective rate, which is competitive with many advisory fees. Current details at trustetc.com.

Rocket Dollar offers both self-directed IRA and Solo 401(k) with checkbook control, meaning you write checks directly from the account without custodian approval on each transaction. Silver plan: approximately $360 setup plus $30 per month. Current pricing at rocketdollar.com.

Alto IRA is a lower-cost self-directed IRA platform starting at $10 to $25 per month. It partners with alternative investment platforms to simplify deal access. Alto focuses on IRA accounts and does not currently offer a Solo 401(k) product. If you need a Solo 401(k) with alternative investment support, Alto is not the right fit.

Verify current pricing with any custodian before committing. Fintech pricing changes, and published fee schedules in any article may not reflect the current rate.

The UBTI/UBIT Issue: Leveraged Real Estate and the IRC 514(c)(9) Exemption

If you plan to invest in leveraged real estate through your retirement account, the account type is not a style preference. It is a tax decision with real dollar consequences.

When an IRA uses debt financing to buy real estate, the income from the borrowed portion is classified as Unrelated Debt-Financed Income (UDFI), a subset of Unrelated Business Taxable Income (UBTI). The IRA owes tax on that income at trust rates up to 37%. The IRA must file Form 990-T using its own Employer Identification Number when gross UBTI exceeds $1,000 in a year. This tax erodes a significant portion of the return that the tax-sheltered structure was supposed to protect.

Solo 401(k) plans are exempt from this tax. IRC Section 514(c)(9) specifically carves out qualified retirement plans from UBTI on leveraged real estate. The same syndication investment that triggers a tax bill inside your SEP-IRA generates zero UBIT inside a Solo 401(k). The exemption is structural and does not depend on which custodian you use.

Two precision points matter. First, the IRC 514(c)(9) exemption applies specifically to leveraged real estate. If you invest in an operating business through an LP interest, income passed through that LP may still generate UBTI inside a Solo 401(k). This is not a blanket UBIT shield. Second, if your investment uses no debt financing, neither account type owes UBIT regardless of asset class.

Deadline Differences: Why December 31 Is the Line That Matters

To make employee elective deferrals for a given tax year, your Solo 401(k) plan must be established by December 31 of that year. Per IRS guidance on one-participant 401(k) plans, if you realize in March that you should have had a Solo 401(k) last year, you cannot create employee deferral capacity retroactively. You may still make employer profit-sharing contributions by the extended filing deadline, but you lose the $24,500 deferral, which is the entire source of the Solo 401(k)'s contribution advantage over the SEP-IRA.

The SEP-IRA operates on a completely different timeline. IRS Publication 560 states directly: "You can set up a SEP plan for a year as late as the due date (including extensions) of your income tax return for that year." For a sole proprietor who files an extension, that means you can open and fully fund a SEP-IRA as late as October 15 of the following year. If you had a strong income year and realized it only in August, the SEP-IRA is still available to you.

For self-employed individuals who tend to file late or remain uncertain about year-end income, this deadline difference is decisive. The SEP-IRA functions as a tax-planning safety net that stays open well into the following year. The Solo 401(k) requires a December 31 decision that commits you to the administrative structure before you know your final income.

Which Account Wins for Your Situation

Choose the Solo 401(k) if you:

• Have net self-employment income above approximately $60,000 and want to maximize tax-deferred savings
• Are willing and able to establish the plan before December 31 of the current tax year
• Want a Roth employee deferral option or expect Roth catch-up contributions
• Are age 50 or older and want catch-up contributions ($8,000 additional, or $11,250 at ages 60 to 63)
• Plan to invest in leveraged real estate and want to avoid UBIT under IRC 514(c)(9)
• Have no non-spouse W-2 employees now and do not expect to hire any

Choose the SEP-IRA if you:

• Missed December 31 and need a prior-year contribution before your October 15 extension deadline
• Want zero ongoing administration with no plan documents, no Form 5500-EZ, and no annual filings
• Have net income above $300,000 where the employer contribution alone approaches the $72,000 cap, reducing the value of the employee deferral
• Expect to hire employees, since a Solo 401(k) becomes ineligible once you have non-spouse W-2 employees

On running both simultaneously: You can legally maintain a SEP-IRA and a Solo 401(k) for the same self-employment income, but the $72,000 Section 415 limit applies in aggregate. Contributing to both does not raise your ceiling. There is rarely a practical reason to maintain both. If you are in this situation, work with a CPA or tax attorney before making contributions to either account in the same year.

At income levels between $60,000 and $300,000, the Solo 401(k) wins on contribution capacity in nearly every scenario. The SEP-IRA wins on simplicity and deadline flexibility. If you plan ahead, have no employees, and want the most tax-deferred room possible, the Solo 401(k) is the right answer. If you prefer the simplest possible structure or missed December 31, the SEP-IRA still delivers a meaningful deduction with none of the ongoing obligations.

Disclosure

This article is for informational purposes only and does not constitute tax, legal, or investment advice. Contribution limits, catch-up figures, and filing requirements are based on IRS Notice 2025-67 and IRS Publication 560 as of the publication date of this article. Tax rules change and individual circumstances vary. The contribution math presented assumes a sole proprietor with no W-2 income from a separate employer and no non-spouse employees. Readers with W-2 employment should account for the per-person 401(k) deferral aggregation rule before projecting Solo 401(k) contributions. Custodian fees and product offerings referenced are based on publicly available information and may have changed. Consult a qualified CPA or tax attorney before establishing or funding any retirement plan.

Author Disclosure: Jeff Barnes, MBA has no personal position in any company, fund, or platform named in this article. Angel Investors Network has no current commercial relationship with any party mentioned. AIN provides marketing and education services, not investment advice. Past performance does not guarantee future results. All investments involve risk, including loss of principal.