Amortization Schedule Calculator

The most counterintuitive thing about amortized loans is how interest-heavy early payments are. On a $400,000 30-year mortgage at 7%, your monthly payment is $2,661. In month 1, $2,333 goes to interest and only $328 goes to principal. It's not until roughly year 21 that the split crosses 50/50.

This isn't the bank tricking you — it's pure math. Interest is charged on the outstanding balance, and at the start your balance is $400,000. Month 1 interest = $400,000 × (0.07 ÷ 12) = $2,333. As the balance slowly decreases, so does the interest charge. The payment stays constant, so more and more of it goes to principal over time.

Understanding this front-loading helps you recognize the real cost of refinancing. If you're 10 years into a 30-year mortgage and you refinance into a fresh 30-year loan, you restart the amortization clock — paying heavy interest again on a still-large balance. The schedule tab makes this tradeoff visible in concrete dollar terms.

Because every dollar of principal you pay reduces the base on which future interest is calculated, extra payments create a compounding benefit. Pay $200 extra in month 1, and you don't just eliminate that month's small principal payment — you shift the entire schedule forward, eliminating all the interest that would have accrued on that $200 for the remaining life of the loan.

On a $350,000 30-year mortgage at 7%, adding just $200 per month cuts over 5 years off the loan and saves roughly $100,000 in interest. That's a return of $100,000 on an additional $13,200 contributed in the first year alone — far better than most savings accounts.

The key insight is that early extra payments are worth far more than later ones. A $1,000 extra payment in year 1 saves roughly $5,000 in total interest over a 30-year loan at 7%. The same $1,000 paid in year 25 saves only about $200. Front-load your extra payments whenever cash flow allows.

The 30-year mortgage offers a lower monthly payment, making it accessible to more buyers. But the amortization schedule reveals the true cost. On a $400,000 loan at 6.5%, a 30-year mortgage costs approximately $252,000 more in total interest than a 15-year mortgage on the same loan amount.

The 15-year schedule moves through the interest-heavy phase twice as fast, meaning you build equity rapidly. By the end of year 5 on a 15-year loan, you've paid off roughly 17% of the principal. On a 30-year loan at the same rate, you've paid off only about 7% — a stark illustration of how slowly a long-term amortized loan erodes the balance early on.

The monthly payment difference on a $400,000 loan at 6.5% is approximately $850 per month — $2,534 for the 30-year versus $3,488 for the 15-year. Whether that extra $850 per month is worth saving $252,000 in interest depends entirely on your other financial priorities, your income stability, and the opportunity cost of deploying that $850 elsewhere.

When you refinance, you reset the amortization clock. If you're 10 years into a 30-year mortgage and you refinance into a new 30-year loan — even at a lower rate — you're now paying 40 years total. The amortization schedule helps you evaluate this tradeoff concretely.

Compare the total remaining interest on your current loan schedule to the total interest on the proposed new loan. If the new loan has lower payments but more total interest, calculate how many months it takes to break even on the closing costs before you actually come out ahead.

A useful rule of thumb: divide your total closing costs by the monthly savings to get the break-even month count. If you plan to stay in the home beyond that point, refinancing makes mathematical sense. The Schedule tab shows your remaining balance at any future date, which is the starting principal for any refinance comparison.

This calculator provides accurate amortization math for standard fixed-rate loans, which cover the majority of residential mortgages. However, adjustable-rate mortgages (ARMs), interest-only loans, balloon payment loans, and loans with prepayment penalties involve additional factors that require professional analysis to evaluate correctly.

Adjustable-rate mortgages, for example, have periodic rate caps and lifetime rate caps that govern how much your payment can change at each adjustment and over the life of the loan. Modeling an ARM accurately requires assumptions about future index rates — something no calculator can reliably project. Similarly, loans with complex fee structures or prepayment penalties change the break-even math in non-obvious ways that deserve professional review before committing.

A HUD-approved housing counselor can provide free or low-cost advice on loan comparisons. For complex refinancing decisions or investment property analysis, a licensed mortgage professional or financial advisor can help you weigh the full picture, including the tax implications of mortgage interest deductions under your specific situation.