RMDs for off calendar plan years

Plan year end is 09/30/2022.  Funds at Nationwide.  Are RMDs done based on 12/31/2021 balance or the 09/30/2021 balance? Thanks in advance! 

If you’re asking what the plan provides, Read (and interpret) The Fabulous Document.

A typical IRS-preapproved document partially paraphrases and refers to the tax-law rules, including 26 C.F.R. § 1.401(a)(9)-5.

https://www.ecfr.gov/current/title-26/chapter-I/subchapter-A/part-1/subject-group-ECFR6f8c3724b50e44d/section-1.401(a)(9)-5

That rule looks to “the account balance as of the last valuation date in the calendar year immediately preceding that distribution calendar year[.]” Q&A-3(a).

If the plan has valuation dates quarter-yearly or more often, it seems likely a December-close date fits that description.

Given that the April 1 and December 31 dates in Code Section 401(a)(9) don't depend on the plan year, I would be much surprised if any plan document provided for different dates merely because the plan year is not the calendar year.