Calculadora de Parcelas de Empréstimo — Formula

How Loan Payments Are Calculated

A fixed-rate loan payment stays the same every month, but the split between principal and interest changes. In the first year of a 5-year auto loan, about 60% of each payment goes to interest. By year 4, that flips and most goes to principal. The formula handles this automatically.

The Formula

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

P = Amount borrowed

r = Monthly interest rate (APR / 12 / 100)

n = Number of payments (term in months)

This is the same amortization formula used for mortgages, auto loans, personal loans, and student loans.

When to Use This

Before signing any loan agreement. Plug in the amount, rate, and term to see what you'll actually pay per month. Then try different terms: a 48-month auto loan vs. 60-month vs. 72-month. The monthly payment drops with longer terms, but total interest paid goes up.

What Changes the Payment Most

Interest rate and loan term. On a $25,000 auto loan, the difference between 5% and 8% APR over 60 months is about $40/month, which adds up to $2,400 over the life of the loan. Shortening from 60 to 48 months increases your payment by roughly $100/month but saves over $1,000 in total interest.

Common Mistakes

Confusing APR with the monthly rate. The formula needs the monthly rate, which is APR divided by 12 and then by 100.

Ignoring fees. Some lenders charge origination fees (1-5% of the loan) that effectively raise the cost beyond what the stated APR suggests.

Extending the loan term to get a lower payment without calculating total interest. A 72-month auto loan at 6% costs thousands more in interest than a 48-month loan at the same rate.