Mo. Rev. Stat. § 287.957
The experience rating plan shall contain reasonable eligibility standards, provide adequate incentives for loss prevention, and shall provide for sufficient premium differentials so as to encourage safety. The uniform experience rating plan shall be the exclusive means of providing prospective premium adjustment based upon measurement of the loss-producing characteristics of an individual insured. An insurer may submit a rating plan or plans providing for retrospective premium adjustments based upon an insured's past experience. Such system shall provide for retrospective adjustment of an experience modification and premiums paid pursuant to such experience modification where a prior reserved claim produced an experience modification that varied by greater than fifty percent from the experience modification that would have been established based on the settlement amount of that claim. The rating plan shall prohibit an adjustment to the experience modification of an employer if the total medical cost does not exceed twenty percent of the current split point of primary and excess losses under the uniform experience rating plan, and the employer pays all of the total medical costs and there is no lost time from the employment, other than the first three days or less of disability under subsection 1 of section 287.160, and no claim is filed. An employer opting to utilize this provision maintains an obligation to report the injury under subsection 1 of section 287.380.
§ 287.957, RSMo