When Xiao Li buys a house, he borrows a personal housing loan principal of RMB 6,543,800+0.5 million from the bank with a repayment period of 20 years, using average capital.

The average capital method is to divide the loan principal evenly according to the total repayment months (average capital), and add the monthly interest of the remaining principal in the previous period to form the monthly repayment amount.

According to the above definition, the monthly principal of Xiao Li's loan is: 150000/240=625 yuan;

The payment base is: 50000/625=80 installments;

Residual principal:150000-50000 =100000 yuan;

The interest portion of 1.300 yuan's principal and interest to be repaid this month is: 1.300-625 = 675 yuan;

The current monthly interest rate is: 675/ 100000 = 6.75‰(6.75‰).