Solo 401(k) vs SEP-IRA 2026: Which Saves More Tax?

Solo 401(k) vs SEP-IRA 2026: Which Retirement Account Saves You More Tax?

If you're self-employed — freelancer, independent contractor, sole proprietor, or single-member LLC owner — two retirement accounts dominate the landscape: the SEP-IRA and the Solo 401(k). Both share the same $70,000 maximum contribution limit for 2026, but they reach that limit very differently — and at lower income levels, the difference in how much you can actually contribute (and therefore how much tax you can defer) is substantial.

The core distinction is structural. A SEP-IRA is employer-only: your contribution is capped at 25% of net self-employment income regardless of how high you set it. A Solo 401(k) has two components — an employee elective deferral of up to $23,500 (available in full even at modest income levels) plus an employer profit-sharing contribution of up to 25% of net SE compensation. That employee deferral component is the reason Solo 401(k)s outperform SEP-IRAs at incomes under roughly $140,000.

This guide walks through the contribution formulas, worked examples at five income levels, the administrative differences, and the exact federal income tax savings at the 22% and 24% brackets — all using verified IRS figures from IRS Publication 560 and IRS Retirement Topics. Use our Self-Employment / 1099 Tax Calculator to model your own net income and tax bracket.

SEP-IRA vs Solo 401(k): The Key Structural Difference

Understanding why these two accounts behave differently starts with their structure. Both are designed for self-employed individuals with no full-time employees (other than a spouse), and both grow tax-deferred — but their contribution mechanics are fundamentally different.

SEP-IRA: Employer-Only Contributions

A SEP-IRA treats you as both the employer and the employee — but only allows the employer-side contribution. That contribution is capped at 25% of net self-employment compensation, up to $70,000 for 2026. Net SE compensation is your Schedule C net profit minus the deductible portion of SE tax (the 50% SE tax deduction), then multiplied by a factor that works out to approximately 18.587% of net Schedule C profit for a sole proprietor. There is no employee deferral component and no catch-up contribution for those aged 50 or older.

The practical implication: at $60,000 of net SE income, the maximum SEP-IRA contribution is roughly $11,130 (18.587% × $60,000). That is the ceiling — you cannot contribute more, regardless of your desire to shelter income.

Solo 401(k): Two-Component Structure

A Solo 401(k) — also called an Individual 401(k) or Self-Employed 401(k) — treats you as both an employee and an employer, and allows contributions from both roles:

• Employee elective deferral: Up to $23,500 in 2026 (or $31,000 if age 50+). This is the same limit as a regular workplace 401(k). Critically, you can contribute up to this amount even if your profit is relatively modest — there is no percentage-of-profit cap on the employee component, only that you cannot exceed your actual compensation.
• Employer profit-sharing contribution: Up to 25% of net SE compensation (same formula as SEP-IRA), capped so total contributions do not exceed $70,000.

At $60,000 of net SE income, a Solo 401(k) allows: $23,500 employee deferral + approximately $11,130 employer contribution = $34,630 total — more than three times the SEP-IRA ceiling at the same income. This is the advantage that makes the Solo 401(k) the default recommendation for most self-employed people who haven't yet reached the $70,000 ceiling.

Why the Gap Closes at Higher Incomes

At high income levels, the SEP-IRA employer contribution formula (25% of net SE compensation) alone can reach $70,000. At approximately $280,000 of net SE income, the 25% employer contribution hits $70,000 — meaning both a SEP-IRA and the employer portion of a Solo 401(k) would both max out. Below that threshold, the Solo 401(k)'s employee deferral gives it a large lead. The crossover point where both plans produce similar maximum contributions is around $135,000–$145,000 of net SE income.

SEP-IRA: Simpler Setup, Good for High Earners

The SEP-IRA is the most popular retirement account for self-employed individuals — primarily because of how simple it is to establish and maintain. There is no plan document, no annual IRS filing, and no December 31 deadline to worry about.

How to Open and Fund a SEP-IRA

A SEP-IRA can be opened at any major brokerage — Fidelity, Vanguard, Schwab, and Charles Schwab all offer no-fee SEP-IRA accounts. The process takes approximately 15 minutes online. There is no annual form to file with the IRS. You simply contribute and invest, and the brokerage reports your contributions on Form 5498.

The SEP-IRA's standout flexibility: you can open a SEP-IRA and make your contribution for the prior tax year up to the due date of your return including extensions. For a sole proprietor or single-member LLC who files for an extension, that means you have until October 15 to both open and fund a SEP-IRA for the previous calendar year. This makes the SEP-IRA ideal for self-employed individuals who don't know their final income until they are preparing their return.

Contribution Formula at Key Income Levels

The precise SEP-IRA contribution formula for a sole proprietor is: multiply net Schedule C profit by 0.9235 (the SE tax multiplier) to get net earnings from self-employment. Then multiply that by 0.5 and multiply by 0.153 to get SE tax. Subtract 50% of that SE tax from net earnings to get net SE compensation. The SEP-IRA limit is 25% of that figure — which simplifies to approximately 18.587% of net Schedule C profit.

Example at $200,000 net Schedule C profit:

• Net earnings from SE: $200,000 × 0.9235 = $184,700
• SE tax: $184,700 × 0.153 = $28,259
• 50% SE deduction: $14,130
• Net SE compensation: $200,000 − $14,130 = $185,870
• SEP-IRA max: 25% × $185,870 = $46,468

At this income level, the SEP-IRA produces a strong contribution — and since the employer portion of a Solo 401(k) uses the same 25% formula, the difference at $200,000 is minimal (a Solo 401(k) already has the employee deferral headroom absorbed by the employer contribution approaching $46,468, with the $70,000 ceiling not yet hit).

Who the SEP-IRA Is Best For

• Self-employed individuals who want maximum simplicity and minimum administration
• Those who need to open a retirement account late in the year or after December 31
• High earners (net SE income above $140,000) where the SEP-IRA approaches the $70,000 ceiling and the Solo 401(k) advantage shrinks
• Those who already have a day job with a 401(k) and want a separate vehicle for self-employment income (note: the $70,000 total limit applies across all accounts from the same employer, but your self-employed and day-job plans are separate)

Source: IRS Publication 560 — Retirement Plans for Small Business.

Solo 401(k): More Complex but Higher Limit at Lower Income

The Solo 401(k) requires more setup effort than a SEP-IRA but pays off substantially for self-employed individuals with net income below the $140,000 crossover point — and for those aged 50 or older who want the catch-up contribution.

The Employee + Employer Structure in Detail

The Solo 401(k) has two contribution buckets:

Employee elective deferral (traditional or Roth): Up to $23,500 in 2026. This is taken from your compensation (net SE income) dollar-for-dollar — not as a percentage. If your net SE income is $40,000, you can contribute $23,500 as an employee deferral. The remaining $16,500 of net income is all that's available for the employer profit-sharing component. This bucket is what makes the Solo 401(k) so powerful at moderate incomes. If you're age 50 or older, the deferral limit rises to $31,000 (the $23,500 base plus $7,500 catch-up).

Employer profit-sharing contribution: Up to 25% of net SE compensation (the same formula as SEP-IRA). Combined with the employee deferral, total contributions cannot exceed $70,000 ($77,500 if age 50+).

Example at $60,000 Net SE Income

*Net SE compensation at $60,000 gross: $60,000 − ($60,000 × 0.9235 × 0.153 × 0.5) = approximately $55,725. Employer contribution = 25% × $55,725 = $13,931. Employee deferral cannot exceed actual net SE income less employer contribution. Combined figure is illustrative — exact amounts depend on your specific Schedule C figures.

The December 31 Deadline

Unlike a SEP-IRA, a Solo 401(k) plan must be established by December 31 of the tax year for which you want to make contributions. The plan document must be signed and the plan formally adopted before year-end. If you miss this deadline, you cannot retroactively open a Solo 401(k) for that year. Once the plan is open, contributions (both employee and employer) can be made up to the filing deadline.

The employee deferral election must also be made before December 31 — you need a written election in place by year-end to contribute as an employee. Employer contributions are more flexible and can be made up to the return due date.

Administration: Form 5500-EZ

Solo 401(k) plans with total plan assets exceeding $250,000 must file Form 5500-EZ with the IRS annually. This is the main administrative burden versus a SEP-IRA. If your Solo 401(k) balance is below $250,000, no annual filing is required. Most brokerage custodians (Fidelity, Schwab, TD Ameritrade) will send you a reminder when your balance approaches the threshold. The form itself is relatively straightforward, but it is an obligation you need to track.

Who the Solo 401(k) Is Best For

• Self-employed individuals with net SE income below $140,000 who want to maximise contributions
• Those aged 50 or older who want the $7,500 catch-up contribution (SEP-IRA offers no catch-up)
• Contractors who want a Roth option — some Solo 401(k) plans allow Roth employee deferrals (tax-free growth), which is not available in a SEP-IRA
• Those who set up their plan before December 31 and can accept the Form 5500-EZ filing obligation when assets exceed $250,000

Source: IRS — Retirement Plans for Self-Employed People.

Side-by-Side Comparison at Five Income Levels

The table below shows the approximate maximum contribution for a SEP-IRA versus a Solo 401(k) at five net self-employment income levels for 2026. All figures assume the taxpayer is under age 50 (add $7,500 to Solo 401(k) totals for those 50+) and use the simplified formula (25% of net SE compensation ≈ 18.587% of net Schedule C profit for the employer component).

Note: At $200,000, total Solo 401(k) = $60,670 — still below the $70,000 ceiling. The gap remains $23,500 at all income levels until the employer component alone approaches $46,500, at which point adding the employee deferral would exceed $70,000 and the employee contribution becomes limited. The plans converge at the $70,000 ceiling at approximately $280,000 of net SE income.

The Age 50+ Advantage

For self-employed individuals aged 50 or older, the catch-up contribution makes the Solo 401(k) advantage even more pronounced. The 2026 catch-up contribution is $7,500, bringing the employee deferral to $31,000 and the total cap to $77,500. SEP-IRAs have no catch-up provision at any age. At a net SE income of $80,000, an over-50 Solo 401(k) participant can contribute $31,000 (employee) + $14,870 (employer) = $45,870 versus $14,870 in a SEP-IRA — a gap of $31,000.

When to Reconsider and Use SEP-IRA Instead

Despite the Solo 401(k)'s contribution advantage, the SEP-IRA wins on simplicity in certain scenarios:

• You discover late in the year that you've had a good income year and haven't set up a plan — only a SEP-IRA can be opened after December 31 for the prior tax year.
• You have variable income year to year and don't want the obligation of maintaining a formal plan document and potentially filing Form 5500-EZ.
• Your net SE income is above $280,000 — at that level, the 25% employer contribution alone reaches $70,000, and both accounts produce the same maximum contribution.

Tax Impact: How Much These Accounts Actually Save

Both SEP-IRA and Solo 401(k) contributions are deducted from adjusted gross income — they reduce federal and state income tax at your marginal rate. Critically, retirement contributions do not reduce self-employment tax: the SE tax base (net earnings from self-employment × 92.35%) is fixed before retirement contributions are deducted. The tax savings are purely from reduced income tax.

Federal Income Tax Savings by Bracket

Every dollar contributed to either a SEP-IRA or Solo 401(k) reduces federal taxable income by one dollar. The income tax saving is therefore your marginal rate applied to the contribution:

Worked Example: $120,000 Net SE Income, 24% Bracket

SEP-IRA path:

• Maximum SEP-IRA contribution: ~$22,300
• Federal income tax saving: $22,300 × 24% = $5,352
• California state tax saving (9.3%): $22,300 × 9.3% = $2,074
• Total combined saving: $7,426

Solo 401(k) path:

• Maximum Solo 401(k) contribution: ~$45,800 ($23,500 employee + ~$22,300 employer)
• Federal income tax saving: $45,800 × 24% = $10,992
• California state tax saving (9.3%): $45,800 × 9.3% = $4,259
• Total combined saving: $15,251

The Solo 401(k) produces $7,825 more in annual tax savings at this income level in California — all from the extra employee deferral capacity.

Long-Term Compounding Effect

The tax savings compound in two directions. First, contributing more dollars now means more capital invested tax-deferred — at 7% annual growth, $45,800 invested instead of $22,300 doubles the compounding base from year one. Second, the tax dollars saved are not consumed by the IRS but can be reinvested or used for other purposes. Over a 20-year career, the difference between consistently maxing a Solo 401(k) versus a SEP-IRA at $120,000 of net income compounds into a substantially different retirement balance.

State Income Tax Bonus

In states with income tax, retirement contributions reduce state taxable income as well. The states with the highest rates — California (up to 13.3%), Hawaii (up to 11%), New Jersey (up to 10.75%), Oregon (up to 9.9%) — amplify the savings significantly. In a zero-income-tax state (Florida, Texas, Nevada, Washington, Wyoming, Alaska, South Dakota), the total saving is the federal rate only. Per our Best States for 1099 Contractors guide, state tax can materially affect which retirement account strategy produces the best net-of-tax outcome.

Source: IRS Retirement Topics — 401(k) and Profit-Sharing Plan Contribution Limits.