Online Amortization Schedule

Think of your loan balance as a bucket that drains slowly, but the lender charges rent on however much water remains. Every month you pay the rent first, then whatever is left over drains the bucket. Early in the loan the bucket is full, so rent is high and drainage is slow. By the final years almost all of your payment is draining the bucket because you are only being charged rent on a nearly empty one.

This mechanism — called amortization from the Latin for killing off — is designed so the lender receives predictable payments and you carry a gradually decreasing debt. The monthly payment amount is set at the start so the bucket reaches exactly zero on the last payment date. What changes each month is only the split between interest and principal, not the total you owe.

The full amortization schedule makes that shift visible. In the early months of a 30-year mortgage the interest share dominates. Midway through the loan the split is roughly even. In the final years nearly every dollar you send reduces principal directly. Understanding this curve is why financial advisors focus on the rate and term as much as the purchase price when evaluating affordability.

Use this tool when you are evaluating a loan offer and want to understand the true cost of borrowing — not just the monthly payment but the total interest across the full term. It is particularly useful before committing to a term length, since a 15-year versus 30-year comparison at the same rate shows dramatically different interest totals. Use it again after receiving a payoff quote to verify your remaining balance matches what the schedule predicts.

It is also the right tool when you are planning extra payments and want a concrete answer to how many months and how many dollars the extra contribution saves. The provisional result appears as soon as you enter the three required fields; the extra payment field refines it without changing the core calculation.

This tool is not the right fit when your loan has a variable or adjustable rate, graduated payments, or an interest-only phase. Those structures require a schedule that recalculates the payment periodically and cannot be expressed with a single fixed payment formula. Similarly, if your loan has prepayment penalties, consult your loan documents before relying on the interest savings estimate from extra payments — the penalty may offset the savings at certain payoff windows.

Confusing the interest rate with the APR. Lenders quote two rates: the note rate used to calculate your monthly payment, and the APR which folds in fees and closing costs. This tool uses the note rate. If you enter the APR instead, your computed payment will be slightly higher than your actual contractual payment. Use the rate on your promissory note or rate lock letter, not the APR disclosure.

Assuming extra payments automatically reduce the term. Whether an extra payment shortens your loan or lowers future payments depends on how your servicer applies it. Most allow you to designate extra amounts as principal-only, but if you do not specify, the servicer may apply the excess to future scheduled payments instead — which does not compress the schedule the same way. Always mark additional payments as principal reduction with your servicer.

Running the schedule on just the financed amount without property taxes and insurance. The monthly payment this tool calculates covers principal and interest only. For a mortgage, your actual monthly outlay includes property taxes, homeowners insurance, and possibly PMI. These are collected separately as escrow but appear on the same bill. First-time buyers frequently underestimate total housing cost by focusing only on the P&I figure here.

The standard fixed-rate monthly payment formula starts with the monthly interest rate, which is your annual rate divided by 12. Call this r. The number of total payments is your term in years multiplied by 12, which gives 360 for the example loan. The formula raises (1 + r) to the power of 360 to find the compounding factor over the full term.

The monthly payment P is then: P = loan amount times (r times the compounding factor) divided by (the compounding factor minus 1). For the example inputs this produces $1,848.50. At zero percent interest the formula simplifies to loan amount divided by number of periods, which is why the tool handles that case separately.

Each month the interest charge equals the current balance multiplied by r. Subtracting that from the total payment gives the principal reduction for that period. The new balance is the old balance minus the principal reduction. Repeating this for 360 rows produces the complete schedule. Extra payments reduce the balance faster, which compresses all subsequent interest charges and collapses the number of rows needed to reach zero.

The standard amortization formula assumes continuous, equal payments with no timing variation. In practice, servicers apply payments on the exact date received, and a payment arriving two days early can save a small but real amount of daily interest. Some loans use a 365-day simple interest method rather than the calendar-month convention assumed here, which means the schedule diverges slightly from reality whenever months have fewer or more than the average number of days. The divergence is small over a single period but can accumulate to a noticeable difference over a 30-year term if you compare the tool's projected payoff balance against your actual servicer statement. Always reconcile against your official statement annually.