Retirement Plan Deadlines      Deadline to establish the plan Deadline to fund the plan IRA - Traditional or Roth N/A - no documentation needed prior to funding April 15 Simple IRA October 1st December 31 for employees to contribute Tax return due date (extension date if extended) for employer contributions 401-K For Safe Harbor 401-K plans it's October 1st - but some companies set the cutoff earlier so plan on September 1 For Solo 401-K plans it's December 31 December 31 for employees to contribute Tax return due date (extension date if extended) for employer contributions SEP N/A - no documentation needed prior to funding Tax return due date (extension date if extended)