Mo. Rev. Stat. § 408.178

Notwithstanding any other law to the contrary, and provided the debtor agrees in writing, the lender may collect a fee in advance for allowing the debtor to defer monthly loan payments, so long as the fee on each deferred period is no more than the lesser of fifty dollars or ten percent of the loan payments deferred, however, a minimum fee of twenty-five dollars is permitted, and no extensions are made until the first loan payment is collected on any one loan. This section applies to nonprecomputed loans only.