What’s a one-participant or solo 401(k) plan?
It's a traditional 401(k) plan for self-employed business owners with no employees, other than a spouse who works for the business. It has the same rules and requirements as any other 401(k) plan, except it’s exempt from annual discrimination testing.
You wear two hats in this 401(k) plan: employee and employer. You can make contributions to the plan as an employee (elective deferrals) and also as an employer (employer nonelective contributions).
Keep in mind that if you’re employed at another company and participate in their 401(k) plan, your contributions to each plan are combined when determining your annual contribution limit.