S.D. Codified Laws § 11-9-26

For purposes of this chapter, the term, tax increment, is that amount obtained by multiplying the total county, municipal, school, and other local real property taxes levied on all taxable real property within a district in any year by a fraction having a numerator equal to that year's assessed value of all taxable real property in the district minus the tax increment base and a denominator equal to that year's assessed value of all taxable real property in the district. In any year, a tax increment is deemed positive if the tax increment base is less than the aggregate assessed value of taxable real property. A tax increment is deemed negative if the base exceeds the aggregate assessed value.