27 CFR § 41.113
Return periods
April 24, 2020
Except as otherwise provided in §41.114, the periods to be covered in the semimonthly tax returns run from the 1st day of the month through the 15th day of that month, and from the 16th day of the month through the last day of that month.
[T.D. TTB-89, 76 FR 3515, Jan. 20, 2011]