S.C. Code Ann. § 6-1-990

(A) The impact fee imposed upon a fee payor may not exceed a proportionate share of the costs incurred by the governmental entity in providing system improvements to serve the new development. The proportionate share is the cost attributable to the development after the governmental entity reduces the amount to be imposed by the following factors: (1) appropriate credit, offset, or contribution of money, dedication of land, or construction of system improvements; and (2) all other sources of funding the system improvements including funds obtained from economic development incentives or grants secured which are not required to be repaid. (B) In determining the proportionate share of the cost of system improvements to be paid, the governmental entity imposing the impact fee must consider the: (1) cost of existing system improvements resulting from new development within the service area or areas; (2) means by which existing system improvements have been financed; (3) extent to which the new development contributes to the cost of system improvements; (4) extent to which the new development is required to contribute to the cost of existing system improvements in the future; (5) extent to which the new development is required to provide system improvements, without charge to other properties within the service area or areas; (6) time and price differentials inherent in a fair comparison of fees paid at different times; and (7) availability of other sources of funding system improvements including, but not limited to, user charges, general tax levies, intergovernmental transfers, and special taxation.