The $19,500 limit in a 401(k) plan relates to all of the following EXCEPT:

The $19,500 limit in a 401(k) plan specifically refers to the maximum amount an individual can contribute to their 401(k) in a given year, which generally does not take marital status into account. This means that regardless of whether someone is single or married, the contribution limit remains the same.

When considering the other options, the limit is indeed based on the employee's tax year rather than the plan year. This means contributions are counted based on the calendar year for tax purposes. Additionally, the contribution limits apply to the total of all 401(k) plans the employee participates in during the year; if an employee has multiple plans, the combined contributions cannot exceed the limit.

Lastly, even if a participant is a 5% owner of the company and has family members who also participate in the plan, the contribution limit is applied to the individual participant alone. Each participant is subject to the limit regardless of their ownership status or family participation in the plan, which reinforces that marital status does not affect the contribution cap.

Thus, the correct answer highlights that marital status is not a factor in determining the contribution limit for a 401(k) plan.