Section 11-504. Taxable years to which tax applies; tax for taxable years beginning prior to and ending after January first, nineteen hundred sixty-six

(a)  General.  The tax imposed by section 11-503 of this chapter, with
  any modification permitted  by  subdivision  (b)  of  this  section,  is
  imposed  for each taxable year beginning with taxable years ending on or
  after January first, nineteen hundred sixty-six.
    (b) Alternate methods for determining tax for taxable years ending  on
  or  after January first, nineteen hundred sixty-six. (1) The tax for any
  taxable  year  ending  on  or  after  January  first,  nineteen  hundred
  sixty-six  and before December thirty-first, nineteen hundred sixty-six,
  shall be an amount equal to the tax which would have  been  imposed  had
  section  11-503  of  this  chapter been in effect for the entire taxable
  year, multiplied by the number of months (or major portions thereof)  in
  such  taxable  year  which  occur  after December thirty-first, nineteen
  hundred sixty-five and  divided  by  the  number  of  months  (or  major
  portions thereof) in such taxable year.
    (2)  In  lieu  of  the  method  of  computation  of  tax prescribed in
  paragraph one of this subdivision, if the taxpayer  maintained  adequate
  records  for  the portion of any taxable year ending on or after January
  first, nineteen hundred sixty-six,  and  before  December  thirty-first,
  nineteen  hundred  sixty-six,  which  falls  within  the  calendar  year
  nineteen hundred sixty-six,  the  tax  for  such  taxable  year  at  the
  election   of  the  taxpayer  may  be  computed  on  the  basis  of  the
  unincorporated business taxable income which  the  taxpayer  would  have
  reported  had  he or she filed a federal income tax return for a taxable
  year beginning January first, nineteen hundred sixty-six and ending with
  the close of such taxable  year  ending  before  December  thirty-first,
  nineteen  hundred sixty-six.  Such taxable year beginning January first,
  nineteen hundred sixty-six  and  ending  before  December  thirty-first,
  nineteen  hundred  sixty-six  shall  be deemed (unless clearly indicated
  otherwise) to be the taxable year of the taxpayer. For purposes of  this
  paragraph,   the  unincorporated  business  exemptions  allowable  under
  section 11-510 of this chapter, the credit allowable  under  subdivision
  (b)  of  section  11-503  of  this  chapter  and  any net operating loss
  deduction as modified pursuant to subdivision two of section  11-507  of
  this  chapter shall each be reduced by the same part of such exemptions,
  credit, or net operating loss deduction (as the  case  may  be)  as  the
  number  of  months  (or  major  portions  thereof)  in  the taxable year
  occurring before January first, nineteen hundred  sixty-six  is  of  the
  number  of  months  (or  major  portions  thereof) in such taxable year.
  Except as provided in paragraph two, the  tax  for  such  period  ending
  before  December  thirty-first,  nineteen  hundred  sixty-six,  shall be
  computed in accordance with the other provisions of this chapter.