Retirement Plans for Freelance Developers: Solo 401(k), Roth Options, and the Mega Backdoor

Freelance web developers and software engineers with no employees (other than a spouse) have access to the Solo 401(k), which offers the highest contribution limits and the most flexibility of any small business retirement plan. The combination of employee deferrals, employer contributions, and (in some plans) after-tax contributions with in-plan Roth conversions makes the Solo 401(k) the most powerful retirement vehicle available to solo operators.

How much can a freelance developer actually contribute?

What about the mega backdoor Roth?

Some Solo 401(k) plan documents allow voluntary after-tax contributions (beyond the $24,500 employee deferral and the employer contribution) up to the $72,000 combined limit, with in-plan Roth conversions. This is the “mega backdoor Roth” strategy.

A developer contributing $24,500 (employee deferral) + $33,457 (employer contribution) = $57,957 could add up to $14,043 in voluntary after-tax contributions to reach the $72,000 cap. Those after-tax dollars are immediately converted to the Roth sub-account (in-plan Roth conversion), and all future growth is tax-free.

Not all Solo 401(k) providers support this feature. The plan document must explicitly allow voluntary after-tax contributions and in-plan Roth conversions. Providers that support this include some self-directed Solo 401(k) custodians and certain brokerage plans. Fidelity and Schwab’s standard Solo 401(k) plans do not currently support after-tax contributions.

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What is the mega backdoor Roth strategy for freelance developers?

The mega backdoor Roth allows after-tax contributions to a solo 401(k) above the normal $23,000 employee deferral limit, up to the total annual addition limit ($69,000 in 2024, $76,500 if age 50+). After making the after-tax contribution, you immediately convert it to the Roth portion of the solo 401(k), where it grows tax-free. This strategy is only available if your solo 401(k) plan document permits after-tax contributions and in-plan Roth conversions (not all providers offer this; Fidelity and Schwab do). The contribution amount is limited by the formula: total limit minus employee deferral minus employer profit-sharing contribution. For a freelance developer earning $200,000 net, the math might be: $69,000 total limit minus $23,000 deferral minus about $37,400 employer contribution (20% of net SE income after the SE tax deduction) = about $8,600 available for mega backdoor Roth.

When can a freelance developer make Solo 401(k) contributions?

A freelance developer with an existing Solo 401(k) has to elect employee deferrals, Roth or pre-tax, by December 31. The deposit can wait until the return due date with extensions, along with the employer contribution. For a 2025 sole proprietor who files Form 4868, that’s October 15, 2026.

Developers who went freelance mid-year and never opened a plan still have a path. A sole proprietor with no employees can adopt a Solo 401(k) after year-end and make 2025 deferrals by April 15, 2026, with no extension.

• For 2026 the deferral limit is $24,500 and the combined cap is $72,000. The $11,250 catch-up for ages 60 to 63 sits on top of the cap.
• If you’d rather use an IRA, 2025 contributions are due April 15, 2026 for most people, and the Roth IRA phase-out for single filers runs from $150,000 to $165,000 for 2025.

Should I choose a SEP-IRA or solo 401(k) for my web development business?

The solo 401(k) is more flexible for most web developers. It allows both employee deferrals ($23,000 in 2024, $30,500 if 50+) and employer profit-sharing contributions (20% of net self-employment income after the SE tax deduction), while the SEP-IRA allows only employer contributions (the same 20%). At $100,000 net income, the SEP-IRA caps at about $18,600. The solo 401(k) allows $23,000 plus about $18,600, totaling about $41,600. The solo 401(k) also offers a Roth option (which SEP-IRAs do not), allowing tax-free growth on contributions. The SEP-IRA’s advantage is simplicity: no annual Form 5500 filing, no plan document to maintain, and contributions can be made up to the extended filing deadline. If you plan to do a backdoor Roth IRA conversion, a solo 401(k) is better because you can roll SEP-IRA funds into it, clearing the way for a clean conversion without the pro-rata rule complications.

This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.