Updated August 31, 2026
In this guide
The three components
Interest is charged on capital still owed. Amortization is the part that actually reduces principal. The outstanding balance is what remains after the period's adjustment and payments.
If the monthly rate is i and the opening balance is OB, basic interest is I = OB × i. A larger payment does not necessarily reduce more debt: insurance and fees do not amortize principal.
Calculated example
The module uses BRL 300,000, 360 months and the current median BCB fixed-rate mortgage observation. Its first, middle and final rows are generated at build time by the simulator's own engine.
BCB reference rate for fixed-rate real-estate financing: 2026-07, median of 3 institutions.
Parameters used
- Financed amount
- R$300,000.00
- Term
- 360 months
- Interest rate
- 14.9797% effective per year
- System
- SAC
- Monthly adjustment
- —
- Extra amortization
- —
Calculated results
| Scenario | SAC |
|---|---|
| First payment | R$4,343.33 |
| Last payment | R$844.29 |
| Total interest | R$633,557.33 |
| Total paid | R$933,557.33 |
| Effective term | 360 months |
| Accumulated adjustment | R$0.00 |
Selected installments
| Payment no. | Payment | Interest | Amortization | Closing balance |
|---|---|---|---|---|
| 1 | R$4,343.33 | R$3,510.00 | R$833.33 | R$299,166.67 |
| 12 | R$4,236.08 | R$3,402.75 | R$833.33 | R$290,000.04 |
| 60 | R$3,768.08 | R$2,934.75 | R$833.33 | R$250,000.20 |
| 180 | R$2,598.09 | R$1,764.76 | R$833.33 | R$150,000.60 |
| 360 | R$844.29 | R$9.76 | R$834.53 | R$0.00 |
Reading the schedule
Under SAC, scheduled amortization stays approximately constant. As the balance falls, interest and the payment decline. Read the balance chart with the table: cent rounding may place a small adjustment in the final payment.
To reconcile a lender statement, separate opening balance, monetary adjustment, interest, amortization, costs and closing balance. That prevents an insurance or indexation difference from being assigned to the wrong line.
What may differ in a contract
- A contract may adjust the balance by TR or another index before calculating interest and amortization.
- Insurance, fees and monthly charges may increase the payment without reducing principal.
Limits of this analysis
- The example excludes MIP and DFI insurance, fees, taxes, arrears and renegotiation.
- Actual dates may create proportional interest; this model uses regular monthly periods.
Sources and review
- Central Bank of Brazil — Citizen Calculator · July 27, 2026