Mo. Rev. Stat. § 408.175

If the maturity of a note or loan contract providing for an amount of interest added to the principal of the loan is accelerated, the unpaid balance shall be reduced by the refund of that portion of the amount of interest originally contracted for which would be required for prepayment in full on the date of acceleration, and thereafter the note or loan contract shall bear interest at the rate originally contracted for, computed on unpaid balances for the time actually outstanding from the installment date following the date of acceleration until paid.