Ala. Code § 11-32-25

The amount to be paid to the authority by the principal municipality during each fiscal year shall be ascertained by determining the amount of ad valorem tax collected for the authorizing county within the city limits of the principal municipality, in addition to the amount determined in Section 11-32-30. The principal municipality shall pay to the authority annually from its general funds an amount equal to 10 percent of the ad valorem tax collected by the authorizing county within the city limits of the principal municipality each year.