New York Consolidated Laws, General City Law - GCT § 4. Taxable years to which tax applies;  tax for taxable years beginning prior to and ending after July first, nineteen hundred sixty-six

(b) Alternate methods for determining tax for taxable years ending on or after July first, nineteen hundred sixty-six and on or before June thirtieth, nineteen hundred sixty-seven.  (1) The tax for any taxable year ending on or after July first, nineteen hundred sixty-six and on or before June thirtieth, nineteen hundred sixty-seven shall be the same part of the tax which would have been imposed had section two been in effect for the entire taxable year as the number of months (or major portions thereof) of the taxable year occurring after July first, nineteen hundred sixty-six is of the number of months (or major portions thereof) in the taxable year.  The credit allowed against such tax as provided by section twenty shall be reduced by a fraction the numerator of which is equal to the number of months (or major portions thereof) in such taxable year which occurred before July first, nineteen hundred sixty-six and the denominator of which is equal to 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 (1), if the taxpayer maintains adequate records for any taxable year ending on or after July first, nineteen hundred sixty-six and on or before June thirtieth, nineteen hundred sixty-seven, the tax for such taxable year, at the election of the taxpayer, may be computed on the basis of the city taxable income which the taxpayer would have reported had he filed a return under this local law for the period (referred to in this paragraph as “short period”) beginning July first, nineteen hundred sixty-six and ending with the last day of the taxpayer's taxable year.  If a return for a period of less than twelve months is made under this paragraph (2), the city taxable income for such short period shall be placed on an annual basis by multiplying such income by twelve and dividing the result by the number of months in the short period.  In determining city taxable income under this paragraph (2), the city personal exemptions provided by section sixteen, shall be reduced to amounts that bear the same ratio to the full exemptions, as the number of months in the short period bears to twelve.  The credit allowed against such tax as provided by section twenty shall be reduced by a fraction the numerator of which is equal to the number of months (or major portions thereof) in such taxable year which occurred before July first, nineteen hundred sixty-six and the denominator of which is equal to the number of months (or major portions thereof) in such taxable year.  The tax shall be the same part of the tax computed on the annual basis as the number of months in the short period is of twelve months.  Except as provided in this paragraph (2), the tax for such period ending on or before June thirtieth, nineteen hundred sixty-seven, shall be computed in accordance with the other provisions of this local law.