Given: Billing cycle is thrity days, and the annual percentage rate is 15.77%. Since there are 365 days in a year, you can now see that 365 / 30 = 12.17, divided by the annual percentage rate (15.77% / 12.17) the answer is 1.2958%. Summed up it is 1.30%. So the periodic interest rate is 1.30%.
