S.C. Code Ann. § 38-19-450: Computation of individual assessments.

A member's proportionate part of any deficiency is computed by applying to the premium earned within the twelve-month period on his contingently liable policy or policies the ratio of the total deficiency to the total premium earned during the period on all contingently liable policies. In computing the earned premiums for the purposes of this section the gross premium received by the insurer for the policy must be used as a base, deducting charges not recurring upon the renewal or extension of the policy.

No member may have an offset against any assessment for which he is liable on account of any claim for unearned premium or losses payable.