Ala. Code § 40-18-42 — Time and Methods of Payment of Tax

(a) Time of payment for individuals. In the case of individuals, the total balance of the tax owed after credits for taxes paid through withholding as provided in Section 40-18-78, or through estimated payments as provided in Sections 40-18-82 and 40-18-83, shall be due and payable at the same time as the due date of an original return.
(b) Time of payment for fiduciaries. In the case of fiduciaries, the total amount of the tax imposed by this chapter shall be paid on April 15 following the close of the calendar year or, if the return should be made on the basis of a fiscal year, then on the fifteenth day of the fourth month following the close of the fiscal year.
(c) Time of payment for corporations. In the case of corporations, the balance of the tax owed after credits for taxes paid through estimated payments as provided in Section 40-18-80.1 shall be due and paid at the same time as the due date of an original return.
(d) Voluntary advance payment. The tax imposed by this chapter or any estimated tax payment thereof may be paid, at the election of the taxpayer, prior to the date prescribed for its payment.