26 CFR 41.6071(a)-1 - Time for filing returns.
(a) In general. Except as provided in paragraph (b) of this section, a return described in § 41.6011(a)-1 must be filed by the last day of the month following the month in which -
(1) A person becomes liable for tax under § 41.4481-2(a)(1)(i)(A), (B), or (C);
(2) A person that is liable for tax under § 41.4481-2(a)(1)(i)(D) is notified by the Commissioner that the tax has not been paid in full; or
(3) A transferee described in § 41.4483-3(f) acquires the vehicle.
(b) Certain transit-type buses. In the case of any bus of the transit type, the first taxable use of which in any taxable period occurs prior to the close of the test period (see paragraph (c) of § 41.4483-2) with reference to which liability for the tax on the use of such transit-type bus for such taxable period is determined, the person in whose name the bus is registered at the time of such use shall, after such test period and on or before the last day of the following month make a return of such tax for such taxable period on the use of such transit-type bus.
(c) Effect of sale during taxable period. A person that is liable for tax under § 41.4481-2(a)(1)(i)(A), (B), (C), or (D) after taking into account the modification required under § 41.4481-2(a)(2) is treated as liable for tax under the same provision of § 41.4481-2(a)(1)(i) for purposes of this section.