What you want to ask is what is the interest rate calculator for 4-year property apartment loans? It is a tool to help people calculate the loan interest rate. The 4-year-old apartment loan interest rate calculator is a tool to help people calculate the loan interest rate. When buying a 4-year-old apartment, buyers usually need to apply for a loan, and each loan plan has a different interest rate. Interest rate calculator provides three different interest rate calculation methods-daily interest rate, monthly interest rate and annual interest rate calculator.