(b) Definition of estimated tax and estimated tax surcharge.--The terms "estimated tax" and "estimated tax surcharge" mean the amounts which a taxpayer estimates to be the tax or tax surcharge imposed by section two hundred nine or two hundred nine-B, respectively, of this chapter for the current privilege period, less the amount which it estimates to be the sum of any credits allowable against the tax or tax surcharge, respectively.

(c) Time for filing declaration.--A declaration of estimated tax and a declaration of estimated tax surcharge shall be filed on or before June fifteenth of the current privilege period in the case of a taxpayer which reports on the basis of a calendar year, except that if the requirements of subdivision (a) are first met:

(1) after May thirty-first and before September first of such current privilege period, the declaration shall be filed on or before September fifteenth, or

(2) after August thirty-first and before December first of such current privilege period, the declaration shall be filed on or before December fifteenth.

(d) Amendments of declaration.--A taxpayer may amend a declaration under regulations of the tax commission.

(e) Report as declaration.--If, on or before February fifteenth of the succeeding year in the case of a taxpayer which reports on the basis of a calendar year, a taxpayer files its report for the year for which the declaration is required, and pays therewith the balance, if any, of the full amount of the tax or tax surcharge shown to be due on the report,

(i) such report shall be considered as its declaration if no declaration was required to be filed during the calendar or fiscal year for which the tax or tax surcharge was imposed, but is otherwise required to be filed on or before December fifteenth pursuant to subdivision (c),

(ii) such report shall be considered as the amendment permitted by subdivision (d) to be filed on or before December fifteenth if the tax or tax surcharge shown on the report is greater than the estimated tax or estimated tax surcharge, as the case may be, shown on a declaration previously made.

(f) Fiscal year.--This section shall apply to privilege periods of twelve months other than a calendar year by the substitution of the months of such fiscal year for the corresponding months specified in this section.

(g) Short privilege period.--If the privilege period for which a tax or tax surcharge is imposed by section two hundred nine or two hundred nine-B, respectively, of this chapter is less than twelve months, every taxpayer required to make a declaration of estimated tax or a declaration of estimated tax surcharge for such privilege period shall make such a declaration in accordance with regulations of the commissioner of taxation and finance.

(h) Extension of time.--The tax commission may grant a reasonable extension of time, not to exceed three months, for the filing of any declaration required pursuant to this section, on such terms and conditions as it may require.