Mortgage Amortization Calculator

How Mortgage Amortization Calculator Works

The calculator first computes your standard monthly payment using the amortization formula, then simulates the loan month by month: each period's interest is the current balance times the monthly rate, and the remaining payment (plus any extra payments you specify) goes toward principal, reducing the balance for the next month.

Extra monthly payments and a separate extra annual payment (applied in whichever month you choose) are both added directly to the principal portion of the payment for that period — since they bypass interest entirely, every extra dollar paid early in the loan saves more in avoided future interest than the same dollar paid later, when the balance (and therefore the interest it generates) is already smaller.

The yearly summary table and chart show principal and interest paid each year and the remaining balance, letting you see at a glance how the mix shifts from mostly interest in the early years to mostly principal later on — a shift that happens automatically with any amortizing loan, and even more dramatically with extra payments applied.

Who Uses Mortgage Amortization Calculator and Why

• Generating a full year-by-year schedule to see exactly how much of each payment goes to principal versus interest over the life of a loan.
• Testing how a specific extra monthly payment amount would shorten a 30-year loan's payoff timeline and reduce total interest.
• Deciding between making one lump extra payment annually versus spreading the same total across smaller monthly extra payments.
• Checking the projected payoff date on a mortgage to plan around it for retirement or other long-term financial goals.

Mistakes to Avoid

• Assuming extra payments made later in the loan save as much interest as the same extra payment made early on — because interest each period is calculated on the current balance, an extra dollar applied early avoids paying interest on it for many more remaining months than the identical dollar applied near the end.
• Overlooking that total interest on a long-term, lower-payment loan like a 30-year mortgage can exceed the original loan amount entirely at typical rates — this isn't a calculation error, it's the normal outcome of compounding on a slowly-declining balance over three decades.
• Entering an extra annual payment in the wrong month, which can skew the yearly summary if you're trying to model a specific real-world payment date, like an annual bonus applied in a particular month.

Tips for Best Results

• Even a modest, sustained extra monthly payment tends to save more in interest than an occasional larger lump sum of the same total amount, since it reduces the balance sooner and more consistently.
• Use the yearly summary table to see when the mix flips from mostly-interest to mostly-principal — that inflection point moves noticeably earlier when extra payments are added.

Fixing Common Problems

The total interest number seems impossibly high for my loan amount. — On a long-term loan at a meaningful interest rate, total interest exceeding the original loan amount is common, not a bug — check the yearly breakdown to see how the balance declines slowly at first, which is why interest accumulates so much over the full term.

I'm not sure whether to add my extra payment monthly or as one annual lump sum. — Consistent extra monthly payments generally save slightly more total interest than a single annual payment of the same total amount, since the balance (and the interest it generates) drops sooner and more steadily; try both in the calculator to compare the exact difference for your loan.

Terms Explained

Amortization schedule: A period-by-period breakdown of a loan showing how each payment splits between interest and principal, and the remaining balance after each payment.

Extra payment: Any amount paid beyond the required monthly payment, applied entirely to principal, which reduces the balance faster and cuts future interest accordingly.