S.D. Codified Laws § 58-25-23
The aggregate of the amounts set aside in this reserve in any calendar year pursuant to § 58-25-22 shall be released from the reserve and restored to net profits over a period of twenty years at an amortization rate not to exceed the following formula: thirty-five percent of the aggregate sum on July first of the year next succeeding the year of addition; fifteen percent of the aggregate sum on July first of each of the succeeding two years; ten percent of the aggregate sum on July first of the next succeeding year; three percent of the aggregate sum on July first of each of the next three succeeding years; two percent of the aggregate sum on July first of each of the next three succeeding years; and one percent of the aggregate sum on July first of each of the next succeeding ten years.
SDCL 58-25-23