terminating SEP & starting 401k & SECURE Act

1.  It's my understanding company cannot have both SEP and 401(k) plan in same year (defined for this question as calendar year).

If no contribution has been made for current year in the SEP, can it be terminated as of end of last year and the 401(k) plan then started mid year? Or would the 401(k) have to wait until the next year?

Understood that the PS plan can start up this year since last SEP contribution was for last year.

2. As we know, under SECURE Act, plans can now be started up prior to tax returns filed the next year.  Is there any kind of exception here where an SEP has not been terminated yet, but no contribution has been made for the prior year, so that the PS plan can actually start up and be effective for the prior year?  Otherwise, this provision doesn't particularly benefit employers with SEPs.

I believe that the "exclusive plan rule" applies to SIMPLEs not to SEPs. It is fine to maintain and make contributions to a SEP and a qualified plan in the same year. The one danger is the 415 limitations as the allocations to the two plans have to be aggregated to determine whether a participant has exceeded the 415 limit. The 404 deductibility limits may also present a problem.

Most, maybe all SEP docs will have something in them that says "you can't use this at the same time that you have a qualified plan" or words to that effect.  It means you can't make contributions to both for the same year.  If you pay attention to 415 limits and non-discrimination it is "just" a document issue.  As M.S. Hatlee notes you are probably thinking of the SIMPLE rule.  You don't have to terminate the SEP; just don't contribute to it.

A Form 5305-SEP ( IRS model agreement) cannot be maintained along with another employer plan. But, a prototype SEP could , if not prohibited under the document.

If no contributions are made under a Form 5305-SEP, that does not prohibit the employer from adopting another plan that year.

Appleby - Thank you for the reminder of that funky rule! I knew that at one point but, due to a supply shortage, the neurons that stored that bit of knowledge must have been reused for something else.

TPApril - sorry for my "half" answer!