Although it is generally understood what you mean by "SEP 401(k)," most people in the financial industry seem to be more familiar with "Solo 401(k)" and "Individual 401(k)" since "SEP" is normally associated with IRAs ("SEP-IRA"). To keep this answer as short as possible, there is an assumption that you do NOT have a SIMPLE 401(k) plan.

When deciding how much you want to contribute to your self-employed 401(k), remember that you can contribute as the "employee" as well as the "employer." Because of this distinction, we should look at both the "employee's" and "employer's" limits on contributions.

First, let's look at the "employee" side of contributions: the $5,000 you expect to contribute to your 403(b) plan as an employee will affect how much you can contribute to your Solo 401(k) as an "employee." The limit for 2011 is $16,500 for both your plans ($17,000 for 2012). This means you would be able to contribute up to $11,500 this year to your Individual 401(k) program.

Next, let us see what can happen on the "employer" side of contributions: there is an overall limit of 20% of your total compensation (your job plus your business net earnings). This limit applies no matter how many retirement plans you have in place, and is calculated based on your compensation BEFORE you consider any potential "employer" contributions. The "employer" contribution limit for 2011 is $49,000 ($50,000 for 2012).

So, if you contribute the full $16,500 this year as an "employee" for both companies, you will still have up $49,000 (or 20% of your after-expense earnings, if less) available to be contributed in your favor from your "employers." This means that you will need to be aware of what your part-time employer is putting in for you with your 403(b) plan.

If this seems to be getting a bit too complicated, it may be a good idea to seek the paid advice of a qualified retirement plans specialist, preferably one with the IRS-licensed ERPA (Enrolled Retirement Plan Agent) certification.

*Tax Disclaimer* The above material is not to be construed as a complete analysis of all Tax considerations. The opinion issued should not be used to avoid or evade Taxes, nor should it be relied upon to avoid any proper federal and/or other Tax-related penalties. Accordingly, this material is not intended or written to be used (and a Taxpayer cannot use it) for the purpose of promoting, marketing, and/or recommending to another party any Tax-related matters. Please be aware that Tax laws are subject to change at any time. Consult your trusted independent Tax advisor for the latest information/interpretations of Tax law.