A Solo 401(k) is a retirement plan for self-employed individuals. To hold this type of plan, you must have a business and no employees. You are the administrator of the plan and have full managing responsibility. It allows you to contribute as both an employer and employee, just like traditional 401(k)s. Contributions must be made from earned income. In 2024, the combined employee and employer total contribution limit for the tax year is $69,000 ($73,500 if you're 50 or older).