27 C.F.R. § 19.237 – Special rule for semimonthly filers for the month of September.

(a) Returns required for September. If the proprietor is required to file semimonthly returns as provided in § 19.235(c), there are three return periods during the month of September. The first semimonthly return period is from the 1st day through the 15th day of the month and the return with remittance is due by the 29th of September. The second semimonthly return period for the month of September is divided into two payment periods. The exact dates of these periods depend upon whether the proprietor remits tax payments by EFT.
1. (1) Taxpayments by EFT. If the proprietor remits tax payments by EFT, the two payment periods for the second half of September are from the 16th through the 26th, and from the 27th through the 30th. The return on form TTB F 5000.24 and remittance for the period September 16-26 is due on or before September 29. The return on TTB F 5000.24 and remittance for the period September 27-30 is due no later than October 14.
2. (2) Taxpayment other than by EFT. If the proprietor is not required to pay the distilled spirits tax by EFT, the two payment periods for the second half of September are from the 16th through the 25th and from the 26th through the 30th. The return on TTB F 5000.24 and remittance for the period September 16-25 is due on or before September 28. The return on TTB F5000.24 and remittance for the period September 26-30 is due no later than October 14.
(b) Amount of payment: Safe harbor rule.— (1) EFT Taxpayers. The proprietor satisfies the requirements of paragraph (a)(1) of this section if by September 29 the amount paid is at least eleven-fifteenths (73.3 percent) of the tax liability incurred in the semimonthly return period for September 1-15, and the proprietor also pays any underpayment of tax resulting from the use of the safe harbor rule on or before October 14.
(2) Other than EFT taxpayers. The proprietor satisfies the requirements of paragraph (a)(2) of this section if the amount paid by September 28 is at least two-thirds (66.7 percent) of the tax liability incurred in the semimonthly return period for September 1-15, and the proprietor also pays any underpayment of tax resulting from the use of the safe harbor rule on or before October 14.
(c) Weekends and holidays. If the required tax payment due date for the return period September 16-25 (non-EFT taxpayers) or September 16-26 (EFT taxpayers), falls on a Saturday or legal holiday, the proprietor's return and remittance are due on the immediately preceding day. If the required tax payment due date falls on a Sunday, the proprietor's return and payment are due on the immediately following day.
(d)
Example.Payment of tax for the month of September: (1) Facts. X, a proprietor required to pay taxes by electronic fund transfer, incurred tax liability in the amount of $30,000 for the first semimonthly period of September. For the period September 16-26, X incurred tax liability in the amount of $45,000, and for the period September 27-30, X incurred tax liability in the amount of $2,000.(2) Payment requirement. X's payment of tax in the amount of $30,000 for the first semimonthly period of September is due no later than September 29. X's payment of tax for the period September 16-26 is also due no later than September 29. X may use the safe harbor rule to determine the amount of payment due for the period of September 16-26. Under the safe harbor rule, X's payment of tax must equal $22,000.00, eleven-fifteenths of the tax liability incurred during the first semimonthly period of September. Additionally, X's payment of tax in the amount of $2,000 for the period September 27-30 must be paid no later than October 14. X must also pay the underpayment of tax, $23,000.00, for the period September 16-26, no later than October 14.
(26 U.S.C. 5061)