Your Solo 401k contribution due date depends on whether you have a sole proprietorship or a corporation. If you have a corporation the employee deferral and the employer profit share are due at two different times. It is very important to make your contributions by the correct due date to keep your plan in compliance. So, when exactly are your solo 401k contributions due?
If you have a sole proprietorship the due date for Solo 401k contributions is easy. It is your tax filing due date, usually April 15. If you file for an extension your due date is October 15. Both the employee deferral and employer profit share have the same due date.
If you have a corporation there are two different due dates.
The employee deferral is due by December 31. The DOL requires these contributions made within 7 days of payroll processing, as a safe harbor. Under no circumstances can it exceed the 15th day of the following month. Since contributions are reportable on Form W-2 (due January 31) you absolutely cannot wait until your corporation tax return is due to complete the employee deferral.
The employer profit share must be elected by December 31, but the payment is not required until the tax return due date, usually March 15. If you file for an extension your due date is September 15.
Now you know when your Solo 401k contribution are due and you will never miss this easy compliance task.