Last Updated 12/25/2025
If you participate in both a 403b plan through your day-time employer, and also participate in a solo 401k sponsored by your self-employed business, your annual contributions to both plans may be impacted as described below.
Employee Deferral Limit
The employee deferral limit –that is, the $23,500 for 2025 is aggregated across your day time employer 403b and your self-employed business solo 401k plan. Same is true for employer profit sharing and voluntary after-tax solo 401k contributions–that is, they must also be reduced by any contributions made to your day-time employer 403b plan. As a result, you may not be able to max out your annual solo 401k contributions if you also contribute to a 403b.
Therefore, you cannot make employee contributions at the pretax and Roth solo 401k level if you have already maxed out the employee deferral limit to your day job employer 403b plan.
Voluntary After-Tax Solo 401k Contributions Also Impacted
Just like employee pretax and employee Roth contributions to a 401k including a solo 401k are part of the 402(g) limit, they also apply to 403b annuity contracts. What is more, the 402(g) limit applies on a combined basis to elective deferrals made to a 401(k) plan and 403(b) plan .
As a result, the 403b annuity contract rules indirectly impact the ability to maximize the mega backdoor Roth solo 401k strategy.
The 403(b) annuity contact contributions are required to be aggregated with the contributions the self-employed individual makes to her solo 401k plan for purposes of the 415 annual additions limit. This is due to the
special rule that applies to 403(b) annuity contracts where a participant
who is covered by the 403(b) plan is also in control of a separate company
(in this case, the participant’s self-employed business sponsoring the solo 401 k). In that case, the 403(b) contributions and solo 401k contributions are required to be aggregated for purposes of applying the 415 limit.
special rule that applies to 403(b) annuity contracts where a participant
who is covered by the 403(b) plan is also in control of a separate company
(in this case, the participant’s self-employed business sponsoring the solo 401 k). In that case, the 403(b) contributions and solo 401k contributions are required to be aggregated for purposes of applying the 415 limit.
Illustration
A doctor is employed by a non-profit hospital to which section 501(c)(3) applies and which provides him with a section 403(b) annuity contract, and the doctor also maintains a private practice as a shareholder owning more than 50 percent of a professional corporation, then any qualified defined contribution plan (e.g., a solo 401k plan) of the professional corporation must be aggregated with the section 403(b) annuity contract for purposes of applying the limitations of section 415(c) and §1.415(c)-1.
In sum, the 403b annuity contribution aggregation rule is a 403b regulation not a solo 401k rule. It will be up to the 403b annuity contract provider to monitor the over contribution rules especially if the individual is also contributing to a solo 401k plan since this restriction is imposed by the 403b annuity rules not the solo 401k regulations.
W-2 Job & Solo 401k Eligibility QUESTION
I recently left my job and had a 403b with them. I do consulting work on the side and have a new W2 job? A few questions for you. 1. Even though I have a W2 job, am I still eligible for a solo401k? 2. Can I roll over some of my 403b into a solo401k?
One may certainly set up a Solo 401k based on their self-employment activity (and provided that there are no full-time w-2 employees working for their business) even if they have a w-2 job.
Moreover, such person can rollover funds from a former employer plan including a 403b and we will help guide through the transfer process as part of our services.
Amount of Self-Employment Income for Solo 401k Eligibility QUESTION
Does it matter how much self-employed income I make to be eligible for a solo401k?
There is no minimum self-employed income to qualify provided that such self-employment activity is legitimate and consistent (not just a one-time event).
See more: https://www.mysolo401k.net/
See more: https://www.mysolo401k.net/
4 Comments
Mark, my wife falls into this situation. She has contributed the max 19.5k at her daytime job (403b). Provided she has sufficient income, could she still contribute up to $58k directly into her solo 401k as an employer contribution (without labeling it voluntary after tax)?
No, because of the aggregation rules.
Hi Mark,
I have a somewhat similar situation except my daytime job W2 has a 401k AND 403b. I contribute the max amount to the 401k and the employer puts 35k into the 403b. If I do a solo 401k with megabackdoorroth ira, would my limit be 69 – 23 (401k) – 35 (403b) = 8k? Or is it just 69 – 35 (403b) = 34k?
Because of the 403b rule, you would be limited to the $8K as it applies across the board. The darn 403b aggregation contribution rules apply at both the employee and the employer level and it thus also impacts contributions made to both a traditional 401k and a solo 401k.