While it was created to be (and is) a “simple” retirement account option for employers with fewer than 100 employees (requires very little admin filing and costs to maintain), it is far from being the most “simple” of the three self-employed retirement account options for self-employed individuals, in my opinion.
Separately, you can also match yourself as employer, with two options:
• match the employee contribution on a dollar-for-dollar basis up to 3% of the compensation (not limited by the annual compensation limit), or
• make non-elective contributions of 2% of the employee compensation up to the annual limit of $285,000 in 2020 and $290,000 in 2021.
Similar to the Solo 401K, if you contribute as an employee and participate in any other employer plan during the year (i.e. a 401K in your day job), the total amount of the salary reduction contributions that you can make to all plans you participate in as an employee (including self-employment) is limited to $19,500 in 2020 and 2021.
For example, if you are under age 50 and have contributed $12,000 to your day job employer sponsored 401K, you can then only contribute $7,500 ($19,500 – $12,000) to your SIMPLE IRA as an employee.