Calculadora SAC
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
amort = P/n; juros_k = saldo_k × r; parcela_k = amort + juros_k
About this calculator
The SAC Calculator simulates the Constant Amortization System, widely used in Brazilian real estate financing, especially by Caixa Econômica Federal and other banks. Unlike the Price Table, in SAC the amortization is fixed in each installment, while interest is charged on the decreasing outstanding balance. This results in a declining installment amount over time, starting higher and reducing gradually. The tool allows you to enter property value, down payment, monthly interest rate, and term, calculating all installments, outstanding balance, and total paid.
The calculation is done in three steps for each period: first, the fixed amortization is defined (financed amount divided by the number of months). Then, the month's interest is calculated (previous outstanding balance times the monthly rate). Finally, amortization and interest are added to obtain the installment. The outstanding balance is updated by subtracting the amortization. This process repeats until full payment. The generated spreadsheet shows the month-by-month evolution, facilitating financial planning.
Use this calculator when comparing real estate financing, especially if you plan to amortize the balance faster or prefer higher initial installments that decrease over time. It is ideal for understanding the total cost of financing (sum of all installments) and comparing with other systems, such as the Price Table. It is also useful for simulating scenarios with different terms and rates, helping in decision-making about the best payment plan.
Cautions: the interest rate must be monthly and compatible with the term (e.g., 0.8% per month for 360 months). Check whether the bank uses a nominal or effective rate. SAC can generate higher initial installments, requiring payment capacity. Additionally, the total paid may be lower than in Price, but depends on contractual conditions. Remember to include additional costs such as insurance and bank fees, which are not simulated here.
Frequently asked questions
What is the difference between SAC and the Price Table?
In SAC, amortization is fixed and installments decrease, while in Price installments are fixed and amortization increases. In SAC, you pay less total interest if you pay off early, but the first installments are higher.
Can I use this calculator for vehicle financing?
Yes, as long as the amortization system is SAC. However, many vehicle financings use Price or other systems. Check with the institution.
What does fixed amortization mean?
It means the amount that reduces the outstanding balance is the same in all installments. It is calculated by dividing the financed amount by the total number of months.
How do I calculate the monthly interest rate if I have the annual rate?
Divide the annual rate by 12 to get the approximate monthly rate. Example: 9% per year / 12 = 0.75% per month. But check if the bank uses compound or simple interest.
Is the total paid in SAC always lower than in Price?
Generally yes, because in SAC the larger installments at the beginning reduce the balance faster, generating less interest. But it depends on the rate and term.