(a) Requirement of declaration. -- Every taxpayer subject to tax under this article shall file a declaration of estimated tax for the taxable year if the taxpayer's liability for tax under this article can reasonably be expected to exceed $12,000 for the taxable year. A taxpayer not required by this section to file a declaration and pay estimated tax may elect to so file and pay.

(b) Definition of estimated tax. -- The term "estimated tax" means the amount which a taxpayer estimates to be his liability under this article for the taxable year.

(c) Contents of declaration. -- The declaration shall contain such information as the Tax Commissioner may, by rules or regulations, require, including, but not limited to, such detailed information as may be necessary to estimate the taxpayer's liability under section six of this article.

(d) Time for filing declaration. -- A declaration of estimated tax shall be filed on or before the fifteenth day of the fourth month of the taxable year, for any taxable year beginning after June 30, 1987.

(e) Amendment of declaration. -- A taxpayer may amend his declaration at any time during the taxable year in accordance with regulations prescribed by the Tax Commissioner. If any amendment of a declaration is filed by a taxpayer, the remaining installments, if any, shall be rateably increased or decreased (as the case may be) to reflect any increase or decrease in the estimated tax by reason of such amendment. If any amendment is made after the fifteenth day of the ninth month of the taxable year, any increase in the estimated tax by reason thereof shall be paid at the time of making such amendment.

(f) Payment of estimated tax. -- The estimated tax shall be paid in four equal installments. At the time the declaration of estimated payment is filed, the taxpayer shall pay one fourth of the estimated tax liability for the taxable year. The second, third and fourth installments shall be paid on the following fifteenth day of the sixth, ninth and twelfth months of the taxable year, respectively.

(g) Application to short taxable year. -- This section shall apply to a taxable year of less than twelve months in accordance with regulations of the Tax Commissioner.

(h) Installment paid in advance. -- Any taxpayer may elect to pay any installment of its estimated tax prior to the date prescribed for its payment.