In the IRS instructions for Form 1128, under When to File, it says:
To request a ruling to adopt, change, or retain a tax year, file Form 1128 by the due date (not including extensions) of the federal income tax return for the first effective year.
I also read in Topic No. 301 When, How, and Where to File, "If you use a fiscal year (tax year ending on the last day of any month other than December), your return is due on or before the 15th day of the fourth month after the close of your fiscal year."
Does this mean that the application deadline for changing a tax year is 4 months + 15 days after the end of the new tax year, or after the old one?
For example, suppose one had an old tax year that was the calendar year, January 1 - December 31, with associated tax day April 15, and was changing to a new tax year July 1 - June 30, with associated tax day October 15. For the tax year 2021, taxes would need to be filed for the short year January 1 - June 30, 2021, I believe with a due date of October 15, 2021. But what if the individual/corporation did not know it was necessary to change their tax year until near the old tax day, April
15 18, 2022? Would it be too late to file Form 1128 to change the tax year for 2021?