There are two main qualifications for Solo 401k plan. The first is income from self-employed activity. This self employed activity can be a business of your own, or simply a part time, freelancing work. You can be employed elsewhere, have your site business, and still qualify. The second qualification is owner-only business. This means that, in order to qualify for a Solo401k plan, you cannot have any full-time employees other than business owner and his spouse. A full-time employee is defined as someone who works more than 1000 hours a year for the business.