How to Use the Amortization Calculator
- Enter Starting loan balance ($), Annual interest rate (%), and Loan term.
- Select the Term unit: Years or Months.
- Choose a Payment schedule: Monthly (12/year), Bi-weekly (26/year), Weekly (52/year), Quarterly (4/year), or Annually (1/year).
- Optionally enter Extra payment per period ($, optional).
- Click Calculate to generate the payment statistics and schedule.
Review the Payment Results
Review the scheduled payment per period, total interest paid, total of all payments, and payoff time. The formula and intermediate assumptions appear above a full schedule that splits every payment into Payment, Principal, Interest, and Remaining balance. The schedule is shown in a scrollable table and reflects any extra payment.
How the Calculation Handles Terms and Interest
The calculation assumes a fixed annual rate and principal-and-interest payments. It converts the annual rate to a periodic rate with r = Annual rate / 100 / Periods per year. For a nonzero rate, it uses Payment = Balance x r / (1 - (1 + r)^-n). When the periodic rate is 0, it uses Balance / n instead.
For each period, Interest = Remaining balance x r, Principal = Payment - Interest, and the remaining balance is reduced by the principal. A term in Years is used directly; a term in Months is divided by 12. The result is multiplied by the selected periods per year and converted to a whole number with Math.round(...). The displayed monetary and rate values are formatted to fixed decimal places.
Extra Payments and Final Payment Behavior
Extra payment per period ($, optional) is applied entirely to principal on top of the scheduled payment. This can reduce the balance faster and shorten the schedule. If the remaining balance is smaller than the scheduled payment plus the extra amount, the final payment is adjusted to the amount needed to pay off the balance.
Limits and Available Actions
The calculator accepts a positive balance, a rate from 0 to 100, a positive term, and a nonnegative extra payment. The selected term and schedule must produce between 1 and 4,800 payment periods. Above 4,800 periods, it shows: The loan term and payment schedule combine to too many or too few payment periods. Enter a realistic term.
Use Copy result to copy the summary and complete schedule, or Download result (.txt) to save the same text.
Calculator Privacy Scope
The loan calculation uses the values entered in the calculator fields. The page also has a separate subscription form that sends an entered email to /assets/subscribe.php; that form is separate from the loan calculation.
Frequently Asked Questions
How is the periodic payment calculated?
For a nonzero periodic rate, Payment = Balance x r / (1 - (1 + r)^-n), where r is the periodic interest rate (annual rate divided by 100 and by the number of payment periods per year) and n is the total number of payment periods. When the periodic rate is 0, the calculator uses Balance / n.
How is each period's interest and principal split calculated?
For each period, Interest = Remaining balance x periodic rate, and Principal = Payment - Interest. The remaining balance is reduced by the principal portion before the next period is calculated.
What does adding an extra payment per period do?
Any extra amount entered is added to the scheduled payment each period and applied entirely to principal, which reduces the remaining balance faster. When the remaining balance is smaller than the scheduled payment plus the extra amount, the final payment is adjusted to the amount needed to pay off the balance.
Does this tool use my actual loan or lender data?
No. It only uses the loan balance, rate, term, and payment frequency you type in. It does not fetch live interest rates, credit records, or any lender or account data, and it is not personalized financial advice.
Why does a bi-weekly or weekly schedule show a lower total interest?
More frequent payments reduce the balance more often within a year, so less interest accrues between payments, and (depending on the periods-per-year assumption used) more payments can be made per year than a strict monthly schedule - both effects lower total interest for the same annual rate and term.