Ala. Code § 45-57-242.04: Assessing Penalty and Interest.

Any person, firm, or corporation who fails to pay the tax herein levied within the time prescribed by this part, in addition to the tax, shall pay a penalty of 10 percent of the amount of tax, together with interest thereon at the rate of one-half of one percent per month, or fraction thereof, from the date at which the tax herein levied became payable, the penalty and interest to be assessed and collected as a part of the tax.