; reference month (A) Reference taxable year Except as provided in paragraph (3)(A), the term reference taxable year means, with respect to any taxpayer for any calendar month, the taxpayer's taxable year beginning in the preceding calendar year or, in the case of a taxpayer who did not file a return of tax for such taxable year, the taxpayer's taxable year beginning in the second preceding calendar year. (B) Reference month The term reference month means, with respect to any taxpayer for any calendar month, the most recent of— (i) the last month of the reference taxable year, or (ii) the most recent calendar month, in the case of a taxpayer who provides, through a specified alternative mechanism, information which is sufficient to estimate the taxpayer’s monthly advance amount for such month. (C) Availability of information Any month or year referred to in subparagraph (A) or (B) shall not be taken into account in determining the reference month or reference taxable year with respect to any calendar month unless all relevant information with respect to such month or year is available to the Secretary and the Secretary has adequate time to make estimates under this section on the basis of such information before the beginning of such calendar month. (D) Treatment of insufficient information Except as otherwise provided by the Secretary— (i) if a taxpayer is not described in subparagraph (B)(ii) with respect to any calendar month and did not file a return of tax for either of the 2 taxable years described in subparagraph (A) with respect to such month, the monthly advance amount with respect to such taxpayer for such calendar month shall be treated as zero unless the Secretary determines that the Secretary can make the estimate described in paragraph (1) on the basis of information known to the Secretary which the Secretary determines is reasonably reliable, and (ii) if the taxpayer is not described in subparagraph (B)(ii) and the information on the return of tax filed for either of the 2 taxable years described