Loan Amortization Calculator — Monthly Payment & Full Schedule
Enter your loan amount, interest rate, and term to instantly see your monthly payment, total interest paid, and a complete month-by-month amortization schedule. Works for personal loans, mortgages, auto loans, and Brazilian financing systems (Price and SAC).
No signup required. All calculations happen in your browser — nothing is sent to a server.
How to Use the Loan Calculator
- Select your market — choose Brazil (BRL, Price/SAC), United States (USD), or Europe (EUR) to set defaults that match your local lending environment.
- Enter the loan amount — the principal you are borrowing, before any down payment.
- Set the interest rate — toggle between monthly and annual. Brazilian mortgages typically quote monthly rates; US and European loans quote annual rates.
- Enter the term — the total number of months you will repay the loan.
- Read the results — the three stat cards show total interest, the first payment, and total cost. The amortization table breaks down every month.
- Export — click "Export CSV" to download the full schedule for use in a spreadsheet.
What Is Loan Amortization?
Amortization is the process of paying off a loan through a series of scheduled payments. Each payment covers two things: the interest charged on the remaining balance, and a portion of the original principal. As the balance decreases, the interest portion of each payment shrinks — but for fixed-rate loans, the total payment amount stays the same.
The standard formula for a fixed monthly payment (Price / French method):
M = P × [r(1+r)^n] / [(1+r)^n – 1]
M = monthly payment
P = principal (loan amount)
r = monthly interest rate (annual rate ÷ 12)
n = total number of payments (years × 12)
Example: $20,000 loan at 6% annual interest over 48 months → monthly rate = 0.5%, monthly payment = $469.70, total interest = $2,545.60.
Brazilian Amortization Systems — Price, SAC, and SAM
Most international calculators only support the French (Price) method. Brazilian lending uses three distinct systems, each with a different payment profile:
| System | Payment | Amortization | Interest | Best for |
|---|---|---|---|---|
| Price | Fixed throughout | Increases over time | Decreases over time | Predictable budget (vehicles, personal loans) |
| SAC | Decreasing | Fixed every month | Decreases over time | Lower total cost (real estate / SFH) |
| SAM | Slightly decreasing | Average of Price and SAC | Decreasing | Intermediary option |
SAC vs Price total cost: For a R$250,000 loan at 1.2% monthly over 360 months, SAC typically costs 8–12% less in total interest than Price. Use the side-by-side toggle in this calculator to see the exact difference for your numbers.
Common Use Cases
- Home purchase simulation: Model a 20–30 year mortgage with the SAC system used by Caixa Econômica and Brazil's SFH program, or a standard US 30-year fixed mortgage.
- Auto loan planning: Enter the financed amount after down payment, choose the term (typically 24–60 months), and verify the monthly payment fits your budget.
- Early payoff analysis: Compare what happens when you shorten the term — even reducing from 360 to 300 months can save tens of thousands in total interest.
- Rate comparison: Run the same loan at two different interest rates to quantify exactly how much each percentage point costs over the full term.
- Export for financial planning: Download the amortization schedule as CSV and import it into Excel or Google Sheets for budget modeling.
Frequently Asked Questions
How is the monthly loan payment calculated?
The standard amortization formula is M = P × [r(1+r)^n] / [(1+r)^n – 1], where P is the principal, r is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments. For SAC loans, the amortization is constant (P ÷ n) and the payment decreases each month as the interest on the declining balance falls. This calculator applies both formulas automatically based on the system you select.
What is an amortization schedule and why does it matter?
An amortization schedule is a complete month-by-month table showing, for each payment: the total payment amount, how much goes to interest, how much reduces the principal (amortization), and the remaining balance. It matters because it reveals the true structure of how your debt is repaid — in early months, a surprisingly large share of each payment is pure interest rather than debt reduction.
Why do I pay more interest in the first months of a loan?
Interest is always calculated on the outstanding balance. At the start of a loan, the balance is at its highest, so the interest charge is highest. As you repay principal, the balance falls, and the interest portion of each subsequent payment decreases. This is why making extra payments early in a loan's life saves far more interest than making the same extra payments near the end.
What is the difference between the Price and SAC amortization systems?
Price (French method) uses a fixed monthly payment throughout the loan term. The interest portion is high at first and decreases over time, while the amortization portion is small at first and grows. SAC (Constant Amortization System, widely used in Brazil for real estate) uses a fixed monthly amortization — you repay the same slice of principal every month. Because the balance falls faster, SAC generates less total interest but requires higher payments in early months.
Can I use this calculator for a mortgage?
Yes. Enter the loan amount (purchase price minus down payment), the annual interest rate, and the term in months (15 years = 180, 30 years = 360). Note that this calculator computes principal and interest only — your actual mortgage payment will also include property taxes, homeowners insurance, and possibly PMI, which vary by location and lender.
How do extra payments reduce the total cost of a loan?
Any amount paid above the scheduled installment goes directly to reducing the principal. Because future interest is calculated on the remaining balance, a lower balance means less interest in every subsequent period. This compounding effect means even a modest extra monthly payment — say 10% of the regular installment — can shave months or years off the loan term and save thousands in total interest.
Resources
- Investopedia — Amortization — comprehensive reference on amortization concepts, formulas, and loan types.
- Consumer Financial Protection Bureau — Loan Basics — US government resource on understanding mortgage costs and shopping for loans.
- Banco Central do Brasil — Sistema Financeiro — official Brazilian central bank with current reference rates, SFH rules, and CET regulations.
