Mo. Rev. Stat. § 148.640: Return filed when — extension of time granted when — interest due on late filing, rate.

Every taxpayer shall file a return with the director on or before the fifteenth day of April in each year. The director may grant a reasonable extension of time for filing returns under such rules and regulations as he shall prescribe. Whenever such an extension of time is granted, a taxpayer shall be required to pay as part of any tax due interest thereon at the rate determined by section 32.065 from and after such date until paid.