Schwab Solo Roth 401(k): Limits, Fees, and the Mega Backdoor Gap

What the Schwab Solo Roth 401(k) Actually Offers High-Income Self-Employed Individuals

The Schwab Solo Roth 401(k) lets self-employed individuals contribute up to $69,000 annually in 2024 ($76,500 with catch-up contributions) while sheltering all future growth from taxation. For someone earning $300K+ from self-employment, this is one of the highest-leverage tax tools available. But Schwab's plan has a specific limitation that could cost high earners significantly more.

2024 Contribution Limits for a Schwab Solo Roth 401(k)

According to IRS Notice 2023-75, the 2024 employee elective deferral limit increased to $23,000, or $30,500 for participants age 50 and older. On top of that, you can add an employer profit-sharing contribution of up to 25% of net self-employment income. The combined annual additions limit under IRC Section 415(c) is $69,000, or $76,500 with catch-up contributions.

The Roth designation applies only to the employee elective deferral portion. Employer profit-sharing contributions go in pre-tax regardless of whether you choose Roth or traditional treatment on your deferrals. This is a detail that gets glossed over in most coverage but matters when you're modeling your actual tax-free balance at retirement.

One deadline that catches people every year: the IRS requires that the plan itself be established by December 31 of the tax year for which you want to make employee contributions. Miss that date and you cannot retroactively open the plan for that year. Employer profit-sharing contributions, however, can be made up to the tax filing deadline including extensions, typically October 15 for sole proprietors. Year-end tax planning with a Solo 401(k) requires you to act on plan establishment well before December 31.

The table below shows how contribution capacity scales with income at 2024 limits.

*Net self-employment income after the deductible portion of self-employment tax.

How a Solo Roth 401(k) Differs from a Solo Traditional 401(k) for High-Income Earners

The standard framing is simple: traditional gives you a deduction now, Roth gives you tax-free withdrawals later. For most retail investors, that framing is sufficient. For high earners, it is not.

If you are currently in the 37% federal bracket and expect to be in a materially lower bracket in retirement, the traditional Solo 401(k) produces a larger after-tax outcome. The math is straightforward. But if you are building a $5M+ portfolio and anticipate that tax rates will rise, or that your retirement income from taxable accounts will keep you in a high bracket regardless, the Roth calculus shifts.

The more important consideration at the FATFIRE level is tax diversification. Holding a substantial Roth balance alongside taxable brokerage accounts and pre-tax retirement accounts gives you flexibility to manage your effective rate in any given year. Research published in the Journal of Financial Planning consistently finds that high-income earners with diversified taxable and tax-advantaged accounts benefit most from placing high-growth assets in Roth accounts to maximize tax-free compounding over time.

Schwab's plan allows you to split contributions between Roth and traditional designations within the same plan year. You can run both simultaneously and adjust the allocation annually based on your income, projected tax rates, and current-year planning needs. Understanding Roth deferral mechanics in detail matters here because the split decision compounds over decades.

For a direct comparison of how the Solo Roth 401(k) stacks up against other self-employed retirement vehicles, see the table below.

Does Schwab Charge Fees for a Solo 401(k) Account?

Schwab charges no account opening fees and no annual maintenance fees on its Individual 401(k) plan. That is a genuine advantage over some third-party administrators who charge $500 to $2,000 annually for plan administration.

Where costs do appear: the expense ratios of the funds you select, and any trading commissions on individual securities. Schwab's own index funds and ETFs carry very low expense ratios, and commission-free trading on listed equities and ETFs is standard. For a straightforward portfolio of index funds, the all-in cost at Schwab is effectively zero beyond fund expenses.

The more important fee consideration is what Schwab's plan document does not support, which is covered in the next section.

The Mega Backdoor Roth: Where Schwab's Plan Falls Short

This is the most consequential limitation in Schwab's Solo 401(k) offering, and it is rarely discussed plainly.

The mega backdoor Roth strategy works as follows: a Solo 401(k) plan that permits after-tax (non-Roth) contributions allows you to contribute beyond the standard Roth deferral limit, up to the Section 415(c) annual additions cap. You then convert those after-tax contributions to Roth, either through an in-plan conversion or a rollover to a Roth IRA. In 2024, this could allow an additional $46,000 in after-tax contributions on top of the $23,000 Roth deferral, assuming no employer profit-sharing contribution.

Schwab's current Individual 401(k) plan document does not support after-tax contributions. That means the mega backdoor Roth is not available through Schwab's prototype plan.

Fidelity's self-employed 401(k) plan also does not natively support after-tax contributions through its standard prototype document. To execute the mega backdoor Roth as a sole proprietor, you generally need a custom plan document from a third-party administrator. The annual cost for that administration typically runs $500 to $1,500, but for a high earner who can shelter an additional $46,000 per year in tax-free compounding, the math is not close.

For someone earning $400,000 annually from self-employment, contributing an additional $46,000 per year in after-tax funds and converting them to Roth, compounded at 7% over 20 years, produces roughly $1.9M in additional tax-free assets. Schwab's zero-fee structure does not compensate for that gap if the mega backdoor Roth fits your situation.

If you are evaluating comparing Solo 401(k) providers specifically for mega backdoor Roth access, Schwab is not the right answer without a supplemental third-party plan document.

The Reverse Rollover: Using a Solo 401(k) to Enable Backdoor Roth Conversions

This is a planning strategy that does not get enough attention. If you have substantial pre-tax IRA balances, the pro-rata rule under IRC Section 72 creates a tax problem when you try to execute a backdoor Roth IRA conversion. The IRS treats all your traditional IRA assets as a single pool, so converting a $7,000 non-deductible contribution to Roth triggers tax on a proportional share of your entire pre-tax IRA balance.

The solution is a reverse rollover. You roll your pre-tax IRA funds into your Solo 401(k), which accepts incoming rollovers from IRAs. Once those pre-tax dollars are inside the 401(k), they no longer count in the pro-rata calculation. Your traditional IRA balance effectively goes to zero, and you can execute clean backdoor Roth conversions going forward.

This reframes the Solo 401(k) as something beyond a savings vehicle. It is a tax planning tool that enables other strategies. The Solo 401(k) must accept rollovers (Schwab's plan does), and the funds must be pre-tax IRA assets, not after-tax. Your tax attorney should confirm the mechanics before execution, but this is a well-established strategy with clear IRS support.

Are There Required Minimum Distributions on a Roth 401(k) After SECURE Act 2.0?

Before 2024, Roth 401(k) balances were subject to Required Minimum Distributions at age 73, unlike Roth IRAs. This made rolling a Solo Roth 401(k) into a Roth IRA before RMD age a standard planning move.

SECURE Act 2.0, enacted in December 2022, eliminated RMDs for Roth accounts held inside employer-sponsored plans beginning January 1, 2024. A Solo Roth 401(k) now behaves like a Roth IRA for RMD purposes. You are not required to take distributions during your lifetime.

This changes the estate planning calculus materially. You can leave the Solo Roth 401(k) intact, continue tax-free compounding, and pass the account to heirs. Understanding inherited Roth 401(k) rules matters here because SECURE Act 2.0 also modified the distribution rules for non-spouse beneficiaries. Most non-spouse beneficiaries must deplete inherited retirement accounts within 10 years, though qualified distributions from inherited Roth accounts remain tax-free.

The practical implication: there is less urgency to roll a Solo Roth 401(k) into a Roth IRA before age 73 than there was prior to 2024. The rollover still makes sense in some cases, particularly if you want to consolidate accounts or access Roth IRA-specific rules, but it is no longer a deadline-driven move.

Can You Have Both a Solo Roth 401(k) and a SEP-IRA at the Same Time?

Technically yes, but the combination is rarely optimal. If you have both a Solo 401(k) and a SEP-IRA in the same tax year for the same self-employment income, your total employer contributions across both plans cannot exceed the Section 415(c) limit. You are not doubling your capacity by holding both. You are splitting the same employer contribution ceiling.

The Solo 401(k) is almost always the better structure for high earners because it adds the employee elective deferral on top of the employer contribution. A SEP-IRA only allows employer-style contributions, capped at 25% of net self-employment income. For someone earning $150,000 in net self-employment income, the SEP-IRA maximum is roughly $37,500. The Solo 401(k) gets you to $60,000+ by adding the $23,000 employee deferral.

The combination that genuinely expands capacity is a Solo 401(k) stacked with a defined benefit plan.

How to Coordinate a Solo Roth 401(k) with a Defined Benefit Plan

For self-employed professionals earning $500,000 or more annually, the Solo 401(k) alone is not the most aggressive tax deferral structure available. A defined benefit (cash balance) plan maintained simultaneously with a Solo 401(k) can allow total annual tax-deductible contributions well in excess of $100,000, sometimes approaching $200,000 or more depending on age and income.

The mechanics: the defined benefit plan operates under separate contribution rules from the defined contribution limits that govern the Solo 401(k). You can fund both in the same year. The defined benefit plan contributions are actuarially determined based on your age, income, and the promised benefit at retirement, so older high earners get the largest deductions.

A 55-year-old self-employed consultant earning $600,000 might contribute $30,500 in employee deferrals to the Solo Roth 401(k), $46,000 in employer profit-sharing, and an additional $150,000+ to a defined benefit plan in the same year. The defined benefit contributions are pre-tax, which reduces current taxable income dramatically. The Solo Roth 401(k) deferral builds the tax-free bucket simultaneously.

This combination requires an actuary and a third-party administrator for the defined benefit plan. The annual administration cost runs $1,500 to $3,000. For someone in the 37% bracket contributing $150,000 to a defined benefit plan, the first-year tax savings alone exceed $55,000. This is a core tax planning strategy when you stop working or transition out of high-income years.

Setting Up a Schwab Solo Roth 401(k): What the Process Actually Requires

The mechanics are straightforward. You need an Employer Identification Number from the IRS, which you can obtain online in minutes. You then open the Individual 401(k) account through Schwab, complete the plan adoption agreement using Schwab's prototype plan document, and designate your contributions as Roth or traditional.

The critical operational point: the plan must be established by December 31 of the tax year. If you are a sole proprietor who decides in February that you wanted a Solo 401(k) for the prior year, you cannot open one retroactively. Employee elective deferrals must also be formally elected before year-end. Employer profit-sharing contributions can be made up to the tax filing deadline including extensions.

Schwab's platform gives you access to individual stocks, bonds, mutual funds, and ETFs within the plan. Schwab Intelligent Portfolios is available for automated management if you prefer that approach. The investment universe is broad enough for any standard allocation strategy.

One practical note: if you later determine you need a custom plan document to support after-tax contributions or other features Schwab's prototype does not cover, you can transfer the account to a third-party administrator without triggering a taxable event. The assets move via direct rollover.

Schwab vs. Competitors: Solo Roth 401(k) Platform Comparison

Schwab is a reasonable default for straightforward Solo 401(k) needs, but the choice of provider matters more than most people realize once you factor in plan document features.

E*TRADE's Solo 401(k) prototype plan does support after-tax contributions, which gives it a meaningful structural advantage for high earners pursuing the mega backdoor Roth without the cost of a third-party administrator. The tradeoff is platform quality and investment selection, where Schwab and Fidelity have historically been stronger.

For most self-employed individuals who want a clean, no-cost Roth Solo 401(k) without the mega backdoor Roth complexity, Schwab is a solid choice. For those who want the full contribution capacity, a third-party administrator with a custom plan document is worth the annual fee.

Understanding optimal Roth vs traditional allocation within the plan is a separate decision that depends on your current bracket, projected retirement income, and the composition of your broader portfolio.

Estate Planning and Wealth Transfer with a Solo Roth 401(k)

The SECURE Act 2.0 change on RMDs makes the Solo Roth 401(k) more useful as a wealth transfer vehicle than it was before 2024. Assets compound tax-free without forced distributions during your lifetime, and qualified distributions to beneficiaries are tax-free.

The constraint is the 10-year rule for non-spouse beneficiaries under the original SECURE Act. Most non-spouse heirs must fully distribute inherited retirement accounts within 10 years of the original owner's death. For a Roth account, this is less punishing than for a pre-tax account because the distributions are tax-free, but it does limit the multi-generational compounding that made stretch IRAs so powerful before 2020.

Spouses retain the ability to roll an inherited Solo Roth 401(k) into their own Roth IRA, preserving the full tax-free compounding timeline. For non-spouse beneficiaries, the 10-year distribution window still produces a significant tax-free inheritance, particularly if the account has compounded for decades.

If your primary goal is multigenerational wealth transfer, a Roth IRA may be structurally cleaner than a Solo Roth 401(k) because Roth IRAs have no RMD requirements and the same 10-year rule applies to beneficiaries. Converting your 401(k) to a Roth IRA at or before retirement is worth modeling with your estate attorney, particularly if you have a large Solo Roth 401(k) balance and want to simplify the inheritance structure.

The capital gains tax implications of distributions and conversions should be part of any estate plan that includes substantial retirement account balances. Coordinating the timing of conversions with your overall taxable income in a given year is where the real planning value sits.

Weighing the Schwab Solo Roth 401(k) Against Other Options

Schwab's Solo Roth 401(k) is a well-built, zero-cost platform for self-employed individuals who want straightforward Roth contribution access with a broad investment menu. The plan establishment process is simple, the fee structure is genuinely competitive, and the platform is reliable.

The limitations are specific and material for high earners. No after-tax contribution support means no mega backdoor Roth without a supplemental arrangement. The prototype plan document cannot be customized. For someone earning $300,000 or more from self-employment, these constraints are worth evaluating carefully before defaulting to Schwab on brand familiarity alone.

The Solo Roth 401(k) itself, regardless of provider, is one component of a broader tax structure. Stacking it with a defined benefit plan, coordinating it with backdoor Roth IRA conversions, and positioning it correctly within your estate plan are where the real value accumulates. Reviewing Roth 401(k) vs other retirement options in the context of your full balance sheet is the right starting point before committing to any single vehicle or provider.

References

• Internal Revenue Service -- "Publication 560: Retirement Plans for Small Business (SEP, SIMPLE, and Qualified Plans)" (2024).
• Internal Revenue Service -- "IRC Section 402A: Optional Treatment of Elective Deferrals as Roth Contributions."
• Internal Revenue Service -- "IRS Notice 2023-75: 401(k) Limit Increases to $23,000 for 2024, IRA Limit Rises to $7,000" (2023).
• Internal Revenue Service -- "SECURE 2.0 Act of 2022: Summary of Key Provisions" (2022).
• Charles Schwab -- "Individual 401(k) Plan Features and Disclosures" (2024).
• Journal of Financial Planning -- "Optimal Asset Location and Roth Conversion Strategies for High-Net-Worth Individuals" (2022).
• Internal Revenue Service -- "IRC Section 415: Limitations on Benefits and Contributions Under Qualified Plans."
• Vanguard -- "How America Saves: Small Business Edition" (2023).