Is the property to be rented out or occupied yourself. Please clarify with a tax advisor whether it is possible to deduct the loan interest on the other 2 properties. The difference between the nominal and effective interest rate is what the interest security costs you additionally. It is probably the contract fee of the building savings contracts plus what you do not amortize plus other fees that do not have to be included. The structure cant be terminated within 10 years without a prepayment penalty, and after 10 years, any loan can be terminated. The only difference is that for the building savings contract, the notice period is not 6 months after 20 years. You can calculate what a 0.5% higher interest rate on the total amount over 20 years costs. Special repayments are made into the building savings contract, and for example, from 100,000 upwards, the deposit insurance is no longer sufficient. In comparison, the risk with the salary and the increase of financing the small remaining amount in 20 years further with funds, life/pension insurance, Riester to repay or sell and buy something new.