A school district may choose not to increase its general fund budget of expenditures by the full amount of budget authority for the general fund budget of expenditures as calculated pursuant to section 79-1023. In such cases, the department shall calculate the amount of unused budget authority which shall be carried forward to future budget years. The amount of unused budget authority that may be used by a district in a single school fiscal year to increase its general fund budget of expenditures above the budget authority for the general fund budget of expenditures as calculated pursuant to section 79-1023 shall be limited to two percent of the difference of the general fund budget of expenditures minus the sum of special grant funds, the special education budget of expenditures, and exceptions pursuant to subsection (1) of section 79-1028.01 for the immediately preceding school fiscal year.