Overdue default interest = overdue principal and interest × default interest rate × overdue days, in which the default interest rate is 50% higher than the loan interest rate agreed in the Individual Housing Guarantee Loan Contract entrusted by Beijing Housing Provident Fund Management Center. Take the loan contract annual interest rate of 3.25% as an example. If the overdue principal and interest is 1 0,000 yuan, the penalty interest for one month overdue is about 4 yuan (1 0,000× 3.25% ÷ 360×1.50 %× 30).