When applying for Missouri payday loans, you may wonder what the highest possible interest rate is on a small cash loan. According to Missouri law, interest rates on debt cannot exceed 9%. Of course, if the lender has an agreement in place where you agree and sign to a higher interest rate charge, that is entirely legal. When applying for loans via the Vivapaydayloans.com website, you can expect an interest rate of between 5.99% and 35.99%.