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A monthly loan payment is calculated with the amortization formula M = P x [r(1 + r)^n] / [(1 + r)^n - 1]. P is the principal, r is the monthly interest rate (the annual rate divided by 12), and n is the total number of monthly payments. The result is a fixed payment that covers both the interest due each month and the gradual repayment of the principal.

The interest rate is the cost of borrowing the principal, expressed as a yearly percentage, while the APR also includes lender fees such as origination charges and points. Because the APR bundles in those fees, it is usually higher than the interest rate. This calculator uses the interest rate. When comparing loan offers, compare APRs, since the APR reflects the fuller cost of borrowing.

The principal is the amount you originally borrowed, before any interest is added. Each monthly payment is split between the interest owed for that month and a reduction of the outstanding principal. As the principal falls, the interest portion of each payment shrinks and the principal portion grows, even though the total payment stays the same.

Amortization is the process of repaying a loan through fixed, regular payments that cover both interest and principal. Early in the term most of each payment goes toward interest, because interest is charged on a larger outstanding balance. Later in the term most of it goes toward principal. The payment amount never changes, but its composition shifts steadily.

A longer term spreads the principal across more payments, so each individual payment is smaller, but interest accrues on the outstanding balance for more months, so the total cost rises. A $250,000 loan at 6.5% costs $1,580.17 a month over 30 years and $2,177.77 a month over 15 years. The 30-year loan is cheaper monthly but costs about $318,861 in total interest, against roughly $141,999 for the 15-year loan.

No. It calculates principal and interest only. A real mortgage payment often also includes property taxes, homeowners insurance, and private mortgage insurance (PMI), which lenders typically collect through an escrow account. Those additions can raise the monthly amount by several hundred dollars, so ask your lender for a full payment estimate before budgeting.

With a 0% interest rate the monthly payment is simply the principal divided by the number of months, because no interest accrues. A $250,000 interest-free loan repaid over 30 years works out to $694.44 a month. Genuine 0% offers are almost always promotional, time-limited, and may revert to a much higher rate afterward.

There are three levers: borrow less, secure a lower interest rate, or choose a longer term. Extending the term lowers the monthly payment but increases the total interest paid over the life of the loan. Refinancing can lower the rate, though it usually involves closing costs that take time to recoup. Making extra payments toward principal does not reduce the required monthly amount, but it shortens the term and cuts total interest.