Solo 401(k) Deep Dive: How Employee and Employer Contributions Work Together

The Solo 401(k) is one of the best retirement options for self-employed people, but the contribution rules confuse a lot of freelancers the first time they look them up. The limit is $72,000, yet you also see $24,500 mentioned. Both numbers are right. The Solo 401(k) has two separate contribution buckets, and how much you can shelter depends on how they interact.

This article picks up where last week's overview left off. We'll go deeper on the mechanics of each bucket, walk through the math at several income levels, and cover the deadline rules that trip people up every year.

You Wear Two Hats

When you operate a sole proprietorship or single-member LLC, you are legally both the business owner and an employee of that business for retirement plan purposes. The IRS recognizes this dual role, which is why the Solo 401(k) has two distinct contribution types, each with its own limit and deadline.

A traditional W-2 employee can only access the employee side of this equation. Their employer handles the other bucket independently. As a self-employed person, you control both, and you can fund both simultaneously. That is what creates the high combined ceiling.

The Employee Elective Deferral

The employee contribution is the simpler of the two. You elect to defer up to $24,500 of your compensation into the plan in 2026. Think of it the same way you would a 401(k) contribution at a day job: the money comes out of what you earn and goes directly into the retirement account before income tax applies (for a traditional contribution).

Two details about this bucket:

It is a per-person limit, not a per-plan limit. The $24,500 applies across all 401(k) plans you participate in during the year. If you have a Solo 401(k) and also worked a W-2 job with a company 401(k) earlier in the year, your elective deferrals to both plans combined cannot exceed $24,500. The IRS aggregates them.

Traditional or Roth, your choice. Many Solo 401(k) providers (Fidelity, Schwab, Vanguard) now allow Roth elections for the employee portion. With Roth, you contribute after-tax dollars but all future growth and qualified withdrawals are tax-free. With traditional, you deduct the contribution now and pay taxes on withdrawals in retirement. Which is better depends on your expected tax bracket trajectory. If you expect to be in a higher bracket in retirement, Roth often wins. If you need the deduction now to reduce a heavy current-year tax bill, traditional is usually the right call.

The Employer Profit-Sharing Contribution

In addition to the employee deferral, the business can make a second, separate contribution: a profit-sharing contribution of up to 25% of compensation, which for a sole proprietor works out to 20% of net SE earnings (explained below). This is the same bucket a SEP-IRA offers.

For a W-2 employee, the employer profit-sharing contribution is entirely out of their hands. The company decides whether to contribute and how much. As a self-employed person, you are the company, so you decide.

The employer contribution does not count toward the $24,500 employee limit. It is separate, with its own calculation. The combined total of both buckets cannot exceed $72,000 in 2026 (plus any catch-up if you are 50 or older), but short of that ceiling, both contributions stack independently.

How the SE Tax Math Affects the Employer Calculation

The "25% of compensation" formula that applies to W-2 employees does not translate directly to self-employed income. Two adjustments turn it into the self-employed rate:

Step 1: Deduct half of your self-employment tax. Before calculating your net SE compensation for plan purposes, you subtract the deductible half of your SE tax. This is the same above-the-line deduction you claim on Form 1040, Schedule 1. It reduces your compensation figure before the employer rate applies.

Step 2: Apply 20%, not 25%. For a self-employed person, compensation is also reduced by the contribution itself, so a 25% plan rate becomes 20% of the Step 1 figure (the rate table in IRS Publication 560 shows this conversion). Measured against net profit, that is about 18.6% for anyone below the Social Security wage base ($184,500 in 2026). The "roughly 20% of net profit" shorthand runs a little high but is close enough for early planning.

A Full Worked Example: $95,000 Net Self-Employment Income

Compare that to a SEP-IRA for the same person. A SEP-IRA only has the employer side: $88,288 × 0.20 = $17,658. The Solo 401(k) produces more than double the contribution at this income level because the employee bucket adds $24,500 that a SEP-IRA has no way to accept.

How Contributions Scale Across Income Levels

The employer bucket grows with income while the employee bucket stays fixed at $24,500 (until you hit the $72,000 combined ceiling). The table shows the 2026 math at different income levels:

Note: Employer contribution figures in the table use the 18.59% effective rate for income under the Social Security wage base. Actual amounts will vary slightly based on your exact SE tax calculation.

What If You Can't Afford to Max Both Buckets?

Most freelancers, especially in early years, cannot contribute anywhere near $72,000 a year, and the plan does not require them to. There is no minimum contribution. You can contribute $1,000 one year and $30,000 the next, which pension-style plans do not allow.

When Does the $72,000 Cap Actually Bind?

The combined $72,000 ceiling becomes the binding constraint only at very high income levels. To hit the cap, your employer contribution alone would need to reach $47,500 (which is $72,000 minus the $24,500 employee maximum). Since the employer contribution is about 18.6% of net profit (slightly more once profit passes the Social Security wage base), that requires net SE income of roughly $252,000 or more.

For most freelancers and self-employed consultants earning under $200,000 per year, the effective limit is not the $72,000 ceiling but the employer formula applied to their income. Even well below the ceiling, the employee bucket keeps the Solo 401(k) ahead of a SEP-IRA at every income level in the table.

Roth vs. Traditional for the Employee Bucket

The employer profit-sharing contribution is always pre-tax (traditional) regardless of what you choose for the employee side. The Roth election applies only to your elective deferral.

For most self-employed people who are actively trying to reduce their current-year tax bill, a traditional (pre-tax) election for the employee deferral makes sense. You get the deduction now, which reduces your income tax. It does not reduce SE tax: SE tax is figured on net profit before any retirement contribution, so traditional and Roth deferrals leave your SE tax bill the same.

The Roth election makes more sense if you are in a temporarily low income year, if you expect tax rates to rise significantly in retirement, or if you already have a large traditional tax-deferred balance and want some tax diversification. Neither choice is right for everyone, and a tax professional can model both using your actual numbers.

Setting Up and Funding Your Solo 401(k)

The safest plan is to have the Solo 401(k) established (not just funded) by December 31 of the tax year. Since 2023 there is a first-year exception: IRS Publication 560 lets a sole proprietor with no employees adopt a new 401(k) after year-end, as long as it is adopted by the tax filing deadline without extensions (April 15, 2027 for 2026), and the first-year employee deferrals are deposited by that same date. An extension does not stretch that window, and not every provider processes late adoptions, so December 31 is still the date to aim for.

If you are self-employed and do not yet have a Solo 401(k), open the account before year-end. Fidelity, Schwab, and Vanguard all offer no-fee Solo 401(k) plans. Fidelity and Schwab offer the broadest investment menus and allow Roth employee deferrals. Opening the account takes about 20 minutes online. Funding it can wait until you know your income.