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Mortgage Amortization Calculator
See how each mortgage payment is divided between interest and principal, how the remaining balance changes payment by payment, and how the schedule is grouped into annual summaries. The chart and detailed schedule are estimates, not an actual lender statement.
What the amortization illustration shows
The calculator shows the estimated regular payment, total amount paid, total interest, and the movement from opening balance to closing balance for each payment period. The chart and detailed schedule make it possible to follow the changing split between interest and principal over time.
Mortgage amount means the mortgage principal being modelled. Payments include principal and interest only. Property taxes, home insurance, condominium fees, utilities, and other ownership costs are not included. This calculator does not test mortgage affordability or qualification.
How to use the schedule
Enter the mortgage principal, nominal annual mortgage rate, and an amortization period that can be expressed as a whole number of months. Select monthly, twice-monthly, biweekly, or weekly payments. The entered rate is held constant throughout the illustration.
Use the chart to see the broad change in principal and interest, and the detailed schedule to inspect the opening balance, periodic interest, principal repaid, payment, and closing balance for each period. Annual summaries group consecutive payment periods beginning with the first payment; they are not calendar years or lender statement periods.
The mortgage term is the period during which a mortgage contract is in effect. The amortization period is the total time the repayment plan is expected to take. A mortgage commonly spans multiple contractual terms, and the rate and other terms may change at renewal.
The calculator treats monthly, twice-monthly, biweekly, and weekly payments as ordinary (non-accelerated) payment arrangements. The twice-monthly, biweekly, and weekly amounts are calculated from the unrounded monthly payment; the schedule does not add extra or lump-sum payments.
How the schedule is calculated
- Convert the entered nominal annual rate, compounded semi-annually, to an equivalent monthly rate. Use it to calculate the base monthly payment over the entered number of amortization months.
- Use the unrounded monthly payment as the basis for all ordinary frequencies: use it as-is for monthly payments; divide it by 2 for twice-monthly payments; multiply it by 12 and divide by 26 for biweekly payments; or multiply it by 12 and divide by 52 for weekly payments.
- For each payment period, calculate interest by applying the corresponding periodic rate to the opening balance. Apply the payment first to that interest; the remainder repays principal. Subtract the principal repaid from the opening balance to obtain the closing balance.
- Carry each period's closing balance forward as the next period's opening balance. Continue payment by payment until the balance reaches zero.
- For each complete annual summary, group 12 monthly, 24 twice-monthly, 26 biweekly, or 52 weekly payment periods. The first summary begins with the first payment period, and the final summary may contain fewer periods.
- Limit the final payment to the principal and interest then owing. It may be smaller than the regular payment. Because twice-monthly, biweekly, and weekly amounts are calculated from the monthly payment, payoff may occur shortly before the entered amortization period ends.
- Calculate the total amount paid as the sum of the payments made, including the smaller final payment, and total interest as the sum of each period's interest. Keep unrounded precision internally and display public currency values to the nearest cent.
The schedule is a mathematical illustration based on equally spaced end-of-period payments. It does not reproduce a lender's transaction dates, daily-interest conventions, contractual rounding, or statement layout.
Example
Suppose the mortgage principal is $500,000, the nominal annual rate is 5%, the amortization period is 25 years, and payments are monthly. The estimated payment is $2,908.02. In the first payment, about $2,061.96 is interest and $846.07 repays principal, leaving an estimated closing balance of $499,153.93.
Under those monthly assumptions, the schedule contains 300 payments and total interest of about $372,407.48. With ordinary biweekly payments calculated from the same unrounded monthly payment, the regular payment is about $1,342.17, the schedule ends with a smaller 649th payment of about $779.23, and total interest is about $370,502.38. The difference reflects payment timing and the stated derivation method; it does not mean accelerated or extra payments were added.
How to interpret the schedule and limits
The calculation holds the entered rate constant for the entire amortization. A mortgage commonly spans multiple contractual terms, and the rate, payment, and other terms may change at renewal.
The calculator does not model accelerated weekly or biweekly payments, extra regular payments, lump-sum prepayments, lender prepayment privileges or penalties, payment holidays, lender-specific dates or day-count conventions, or future renewal rates.
Each annual summary groups consecutive payment periods beginning with the first payment. It is not a calendar year, mortgage term year, or lender statement period, and the final summary may contain fewer payment periods.
Displayed amounts are rounded to cents, while the calculation retains greater precision. Because each component and each row is rounded separately, displayed interest and principal may not add exactly to the displayed payment; adding displayed rows or multiplying a displayed payment by a count may also differ slightly from displayed totals.
The chart and amortization schedule are provided for educational purposes. They are neither an actual lender statement nor a mortgage recommendation. Contractual payments, the balance, interest, renewal terms, and prepayment rules are determined by the mortgage contract and lender.