Mo. Rev. Stat. § 303.175: Motor vehicle liability policy, minimum term, exceptions.

Every private passenger motor vehicle liability policy issued to meet the requirements of this chapter shall have a minimum term of three months. Each policy payment collected by the insurer shall be sufficient to pay for at least one month's coverage under the policy, except that this restriction shall not apply to payments on policies made by way of payroll deductions. This section shall not be construed to interfere with the cancellation and renewal provisions of sections 379.110 to 379.120 nor shall it apply to any fleet, rental, group or commercial motor vehicle policy.