The amortization by the French method, progressive or classic, is characterized by the payment of overdue interest, that is to say, at the end of each payment, and payment of constant instalments in each period.
Interest decreases as loan periods pass and amortized capital increases in evey new period.
The follow image contains the formula to calculate a banking loan.
Mês = Month;
Prestação = Payment;
Juros = Interest;
Amortização = Amount amortized;
SD (Saldo Devedor) = Fixed Amount.
You can download the script SQL_CALCULAR_PRICE.sql on my Github, to analyze how to calculate PRICE using T-SQL. Follow the link: