401(k) Plans for Owner-Only Businesses

ERISA consultants at the Retirement Learning Center (RLC) Resource Desk regularly receive calls from financial advisors on a broad array of technical topics related to IRAs, qualified retirement plans and other types of retirement savings and income plans, including nonqualified plans, stock options, and Social Security and Medicare.  We bring Case of the Week to you to highlight the most relevant topics affecting your business.  

A recent call with an advisor in North Carolina is representative of a common question related to owner-only businesses and retirement plans. The advisor asked: “Can an unincorporated, owner-only business have a 401(k) plan and, if so, are there any special considerations of which we need to be aware?” 

Highlights of Discussion  

  • Yes, an unincorporated, owner-only business may have a 401(k) plan—commonly referred to as a(n) “individual (k)” or “solo (k)” plan.   

  • Special considerations with respect to the solo (k) plan include, but would not be limited to, the  

    • Deadline for establishing a 401(k) plan,  

    • Deadline for making a salary deferral election, and  

    • Owner’s compensation for contribution purposes.  

  • The deadline for establishing a 401(k) plan for any eligible business changed beginning in 2021 to the business’s tax filing deadline plus applicable extensions.1 The prior deadline was the last day of the business’s tax year (e.g., December 31 for a calendar year tax year). However, keep in mind the timing of when a salary deferral election must be made has not changed. 

  • Salary deferrals can only be made on a prospective basis [Treasury Regulation (Treas. Reg.) 1.401(k)-1(a)(3)]. Therefore, the salary deferral election must be made prior to the receipt of compensation. For self-employed individuals (i.e., sole proprietors and partners), compensation is considered paid on the last day of the business owner’s taxable year. The timing is connected to when the individual’s compensation is “deemed currently available” [see Treas. Reg. § 1.401(k)-1(a)(6)(iii)]. Therefore, a self-employed person has until the end of his or her taxable year to execute a salary deferral election for the plan (e.g., December 31, 2020, for the 2020 tax year).  

  • The definition of compensation for contribution purposes for an unincorporated business owner is unique [IRC 401(c)(2)(A)(I)]. It takes into consideration earned income or net profits from the business which then must be adjusted for self-employment taxes.  Please refer to the worksheet for calculating compensation for and contributions to a solo (k) plan for a self-employed individual in Publication 560, Retirement Plans for Small Businesses. A business owner who wants to have a 401(k) plan should work with his or her CPA or tax advisor to determine his or her earned income and maximum contribution for plan purposes. 

  • The 2020 contribution for an unincorporated business owner to a solo (k) plan with enough earned income could be as high as $57,000 (or $63,500 if he or she turned age 50 or older before the end of the year). For 2021, those limits are $58,000 and $64,500, respectively.  


Ryan is a sole proprietor who would like to set up a solo k plan effective for 2020.  The IRS extended his tax filing deadline for 2020 to May 17, 2021, and if Ryan files for an extension, his extended tax deadline would be October 15, 2021. Therefore, the latest Ryan could potentially set up a solo k plan for 2020 would be October 15, 2021. Since Ryan is past the deadline for making a salary deferral election for 2020, however, his contribution would be limited to an employer profit sharing contribution based on his adjusted net business income for 2020. The sooner Ryan sets up the solo k for his business, the sooner he will be able to make employee salary deferrals for 2021.  


For self-employed individuals and their tax advisors, there are several special considerations with respect to setting up and contributing to solo (k) plans, including, but not limited to, the deadline for establishing a 401(k) plan, the deadline for making a salary deferral election, and the owner’s compensation for contribution purposes.

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