"In general, the first year of a new safe harbor 401(k) plan must be at least 3 months long ... That means the deadline for employers to adopt a new [calendar-year-based safe harbor] plan is October 1.... The SECURE Act extended the deadline for employers to adopt a new traditional 401(k) plan from the last day of the tax year until the due date of that year's tax return. That means the deadline for employers to adopt a new [calendar-year-based] plan will depend upon their tax status ... Replacing [a SIMPLE IRA] with a safe harbor or traditional 401(k) plan takes some planning ... [A chart provides various] 2020 and 2021 deadlines for [calendar-year-based] plans."  MORE >>