Calculadora de Financiamento Imobiliário — Formula

How Mortgage Payments Work

Your monthly mortgage payment stays the same every month for the life of a fixed-rate loan, but what's inside that payment shifts over time. Early on, most of your payment goes toward interest. By year 20 of a 30-year loan, the split flips and most goes toward principal.

The Formula

M = P * [r(1+r)^n] / [(1+r)^n - 1]

M = Monthly payment (principal + interest only)

P = Loan amount (home price minus your down payment)

r = Monthly interest rate (annual rate divided by 12, then by 100)

n = Total payments (loan term in years times 12)

When to Use This Calculator

Use it when comparing homes at different price points, testing what happens if you put more down, or seeing how a rate change affects your payment. It's also useful for checking whether a 15-year term is affordable vs. a 30-year.

What This Doesn't Include

This calculates principal and interest only. Your actual monthly housing cost will be higher because of property taxes (typically 1-2% of home value per year), homeowner's insurance, and PMI if your down payment is under 20%. On a $300K home, taxes and insurance can add $300-$500/month on top of the P&I number shown here.

What Changes the Payment Most

Interest rate has the biggest impact. On a $240,000 loan, the difference between 6% and 7% is about $160/month, which adds up to $57,600 over 30 years. Loan term is next. A 15-year term roughly doubles your monthly payment but saves you more than half the total interest.

Common Mistakes

Forgetting to subtract the down payment before calculating. The formula uses the loan amount, not the home price.

Comparing rates without checking if they include points. A lower rate with 2 points upfront might cost more than a slightly higher rate with no points.

Not accounting for PMI. If you put less than 20% down on a conventional loan, PMI typically adds 0.5-1% of the loan amount per year to your cost.