27 CFR § 40.163
Semimonthly tax return periods
April 24, 2020
Except as otherwise provided in §40.164, the periods to be covered by semimonthly tax returns are from the 1st day of each month through the 15th day of that month and from the 16th day of each month through the last day of that month.
[T.D. TTB-89, 76 FR 3513, Jan. 20, 2011]