An amortization calculator breaks down every payment you will make on a loan into its two components: the portion that goes toward interest and the portion that reduces your principal balance. By entering your loan amount, interest rate, and term, you instantly receive your fixed monthly payment, the total amount you will pay over the life of the loan, the total interest cost, and a complete amortization schedule - a table showing exactly how each payment is allocated month by month and year by year.
Amortization calculators are used most often for mortgages, auto loans, personal loans, and student loans - any fixed-rate installment loan where payments remain constant throughout the repayment period. The schedule they generate is one of the most useful documents in personal finance: it shows you precisely how slowly your balance decreases in the early years (when most of each payment goes to interest) and how quickly it falls near the end (when most goes to principal).
When you take out an amortizing loan, your lender calculates a fixed monthly payment that will exactly pay off your balance - principal plus all interest - over the loan term. The formula used is:
Monthly Payment = P x [r(1+r)^n] / [(1+r)^n - 1]
Where P is the principal (loan amount), r is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments (years x 12).
Although your payment amount stays the same every month, what happens inside that payment changes dramatically over time. In the first month, nearly all of it covers interest - because the outstanding balance is at its maximum. Each subsequent month, a small amount of principal is paid off, so the balance is slightly lower, which means slightly less interest accrues, which means slightly more of the next payment goes to principal. This self-reinforcing process is what amortization means: the loan gradually extinguishes itself over time.
The amortization schedule generated by this calculator contains four columns for each period:
The annual view aggregates all 12 monthly payments into a single row per year, making it easier to see the big picture: how much interest you paid in a given year (useful for tax purposes), how much principal you repaid, and where your balance stands at year-end.
One of the most eye-opening things about viewing a full amortization schedule is understanding just how much a long loan term costs in total interest. Consider a $300,000 mortgage at 7% APR:
This comparison illustrates why financial planners consistently recommend choosing the shortest term you can comfortably afford, and why extra payments are so powerful. Every extra dollar of principal paid today eliminates not just that dollar but all the future interest that would have been charged on it.
Making extra payments is one of the highest-return financial moves available to homeowners and borrowers. Because mortgage interest is charged on the outstanding balance, reducing that balance even slightly produces compounding interest savings over the remaining loan term.
Example: On a $300,000, 30-year mortgage at 7% APR, adding just $200 per month to your payment cuts 5 years and 8 months off your payoff timeline and saves approximately $98,000 in total interest - a guaranteed 7% return on every extra dollar. This calculator supports three types of extra payments, each with a calendar-based start date so you can model exactly when the extra payments begin:
This calculator models fixed-rate loans, where the interest rate and monthly payment remain constant for the entire term. Adjustable-rate mortgages (ARMs) have an initial fixed period (typically 3, 5, 7, or 10 years) followed by periodic rate adjustments. The initial period of an ARM can be modeled here, but the adjustable portion requires separate modeling because the payment will change with each rate adjustment.
The monthly payment shown in this calculator is principal and interest (P&I) only. Your actual monthly mortgage payment also includes property taxes, homeowner's insurance, and possibly private mortgage insurance (PMI) and HOA fees. These additional costs can add hundreds to thousands of dollars per month to your total housing expense but are not part of the amortization calculation itself.
For borrowers who itemize deductions on their federal tax return, mortgage interest paid during the year may be tax-deductible. The annual table in this calculator shows your total interest paid each year, which matches the figure reported on your Form 1098 from the lender - making it easy to verify or estimate your potential deduction.
Auto loans typically have shorter terms (24 to 84 months) and lower balances than mortgages, but the amortization mechanics are identical. A key consideration for auto loans is equity: in the early months of a long auto loan, you may owe more than the car is worth (negative equity or being "underwater") because the balance decreases slowly while the vehicle depreciates quickly. The amortization schedule shows exactly when your outstanding balance will fall below the vehicle's market value.
In the first month of a 30-year, $300,000 mortgage at 7%, your balance is at its maximum. At 7% annual rate, monthly interest is 0.583% x $300,000 = $1,750. If your payment is $1,996, only $246 goes to principal. As the balance slowly decreases, so does the monthly interest charge, and more of each payment reduces principal.
Look at the annual table generated by this calculator - find the row for the year in question and read the Interest column. This figure should match your Form 1098 from your lender if modeling a mortgage.
No. For most standard amortizing loans, extra payments reduce your balance and shorten your payoff timeline, but your required monthly payment remains the same. You can stop making the extra payments at any time and simply continue with the standard payment.
The interest rate (note rate) is used to calculate your monthly payment and amortization schedule. The APR is broader and includes certain fees spread over the loan term. For the amortization calculation, use the interest rate (note rate), not the APR.
The loan start date determines the calendar dates shown in the monthly table and the start dates for extra payments. It does not affect the payment amount or total interest - it controls the date labels and when extra payments kick in relative to the loan timeline.