(1) Plan 1. Except as provided in subsection (2) of this section, to calculate average final compensation for a member of TRS Plan 1, the department will:

(a) Determine the two consecutive fiscal years in which the member's total earnable compensation is the highest.

(b) Divide the total earnable compensation for this period by twenty-four to determine the member's average monthly compensation during this period.

(2) Plan 1 alternative. Certain members of TRS who have taught in an extended school year program may use an alternate two-year period for the calculation of average final compensation. An alternate period may be used only if a TRS member has rendered service under contract in an extended school year program at any time during the member's career, and under such contract, the member rendered some service in the extended school year program after June 30. The following process is used to determine whether the alternate period is advantageous to the member:

(a) If a member rendered contracted service in an extended school year program after June 30, the department will identify the last day of required service in the district's official calendar for the extended school year.

(b) The alternate period is a two-year period ending on the last day of service in the official calendar.

(c) The department will total the member's compensation for services rendered during the alternate period.

(d) The department will repeat steps (a) through (c) of this subsection for all alternate periods.

(e) To calculate the member's average final compensation, the department will use the member's highest two-year period, as calculated in either subsection (1)(a) or (2)(c) of this section.

(3) Plans 2 and 3. To calculate average final compensation for a member of TRS Plans 2 or 3, the department will:

(a) Determine the sixty consecutive service creditable months in which the member's total earnable compensation is the highest.

(b) Divide the total earnable compensation for this period by sixty to determine the member's average monthly compensation during this period.