What is the Deadline to Establish and Fund a Solo 401k?

In order to take a deduction for a specific year, a solo 401k plan must be established and adopted by the last day of that tax year.  For a calendar tax year, that date is December 31st.

For contributions, you generally can apply them to the prior year if all of the following criteria are met:

  • They are made by the due date of your tax return for the prior year (which includes extensions).
  • The plan treated the contributions as though it had received them on the last day of the previous year.
  • You do one of the following: (1) specify in writing to the plan administrator (or trustee) that the contributions are intended to be applied to the prior year; or (2) you deduct the contributions on your tax return for the prior year.