215 ILCS 5/529.4
Whenever the fund shall assess insurers in accordance with this Section, each insurer may charge an additional premium on every property insurance policy issued by it insuring property in this state, the effective date of which policy is within the 3 year period commencing 90 days after the date of assessment by the Fund. The amount of the additional premium shall be calculated on the basis of a uniform percentage of the premium on such policies equal to 1/3 of the ratio of the amount of an insurer's assessment to the amount of its direct earned premiums for the calendar year immediately preceding the year in which the assessment is made, such that over the period of 3 years the aggregate of all such additional premium charges by an insurer shall be equal to the amount of the assessment of such insurer. The minimum additional premium charged on a policy may be $1.00 and any other additional premium charged may be rounded to the nearest dollar.
215 ILCS 5/529.4