Ala. Code § 45-57-242.04

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.