How to use the mortgage loan calculator
- Enter the property/loan amount and, if applicable, the down payment.
- Enter the annual interest rate and the term in months (for example: 360 months for 30 years).
- Choose the amortization system: SAC (decreasing payments) or Price (more constant payments).
- Click “Calculate” to see payments, interest, remaining balance, and the full amortization schedule.
- Optionally, add extra payments in specific months to simulate reducing the term or reducing the monthly payment.
What is a mortgage loan and how do interest and principal work?
In a mortgage-style loan, you pay for the property over time in monthly installments. Each installment typically includes interest (the cost of borrowing) and principal (the part that reduces the remaining balance).
As months pass, the remaining balance usually decreases. Because interest is calculated on the remaining balance, the interest portion often falls over time, while the principal portion may be constant (SAC) or adjusted to keep payments more stable (Price).
SAC vs Price: what’s the difference?
SAC and Price are ways to distribute interest and principal over time. The total interest paid and the payment profile can change significantly.
SAC system (constant principal)
In SAC, the principal portion is (roughly) constant. Payments typically start higher and decrease over time because interest drops as the remaining balance shrinks.
Price table (more constant payments)
In the Price system, the payment tends to be more constant at the beginning. The composition changes: you pay more interest early on and more principal later.
Tip: use the simulator to compare total interest and the first/last payment under each system.
How to read the amortization schedule
The amortization schedule shows, month by month, how the loan evolves. You will typically see columns such as:
- Opening balance: how much you owe at the start of the month.
- Interest: interest paid that month (calculated on the balance).
- Principal: the part of the payment that reduces the balance.
- Payment: what you pay in that month (by system rules).
- Ending balance: how much you still owe after the month’s payment.
Extra payments: reduce term or reduce payment
Extra payments are additional amounts (on top of the regular payment) that reduce the remaining balance faster. This typically reduces total interest and can shorten the loan.
In this simulator, you can choose the goal of the extra payment:
- Reduce term: keep payments similar and finish earlier (fewer months).
- Reduce payment: aim for lower payments while keeping (roughly) the term.
The exact effect depends on bank rules and your contract. Treat the result as an estimate and confirm the rules with your lender.
Example simulation (and how to interpret the results)
A good simulation helps you compare scenarios and understand the total cost of a loan—not just the monthly payment.
Example (illustrative numbers)
- Loan amount: R$ 500,000
- Down payment: R$ 100,000
- Interest: 10% per year
- Term: 360 months
What to look at
- Total interest paid: helpful to compare SAC vs Price.
- First and last payment: shows the cash-flow profile over time.
- Balance over time: important if you plan to prepay or sell before the end.
Related tools to make better decisions
If you want to go deeper, these calculators can help compare scenarios and understand return/net cost.
Important notice
This calculator is educational and may not include costs like APR/CET equivalents, insurance, fees, taxes, or contract-specific rules. Use it as an estimate and confirm details with your lender.