Mo. Rev. Stat. § 408.320: Buyer may pay retail time contract debt before maturity — refund of charges.

Notwithstanding the provisions of any retail time contract to the contrary, any buyer may prepay in full at any time before maturity the debt of any retail time contract and on so paying such debt shall receive a refund credit thereof for such anticipation of payments. The amount of such refund shall be calculated by the actuarial method. The lender shall retain no more interest than is actually earned whenever a retail time contract is prepaid.