Mortgage Amortization Calculator
Generate a month-by-month amortization schedule for a fixed-rate mortgage. Enter the loan amount, interest rate and term to see the monthly payment, the total interest and how each payment splits into principal and interest. Add an extra payment every month, once a year or one time, and the calculator shows when the loan is paid off, the months you save and the interest you save, next to the same loan without extras. Every row is in whole cents, and the principal column adds up to the loan amount. A 0% rate works too.
How to use the Mortgage Amortization Calculator
- Enter your numbers in the Mortgage Amortization Calculator above.
- Press the Calculate button to see the result.
- To try other numbers, change any value and press the button again.
The amortization schedule logic
Each month: Interest_k = Balance_(k−1) × annual rate ÷ 12, rounded to the cent · · · Principal_k = Payment − Interest_k · · · Balance_k = Balance_(k−1) − Principal_k
The payment comes from the standard annuity formula and is rounded to the cent. The schedule repeats these three steps from month 1 until the balance reaches zero. Every payment but the last is the same. The last one pays its month's interest plus whatever balance the rounding has left, so the schedule ends at exactly 0.00. The interest share shrinks as the balance falls, so the principal share grows. At 0% there is no interest, and the payment is the loan amount divided by the number of months. An extra payment goes on the balance after the regular payment, so all of it is principal, and the next month's interest is charged on the smaller balance. If an extra is more than the balance left, the calculator uses only what clears the loan.
Worked example
On $350,000 at 6.5% for 30 years, the monthly payment is $2,212.24. In month 1, $1,895.83 goes to interest and $316.41 to principal, which leaves a balance of $349,683.59. Payments 1 to 359 are $2,212.24 and the last one is $2,209.89. Over 360 payments you pay $796,404.05, of which $446,404.05 is interest. Add $200 to every payment and the loan is paid off in 286 payments instead of 360, 6 years 2 months sooner. Total interest falls to $338,308.14, which saves $108,095.91.
Frequently asked questions
Why does so little of the first payment go to principal?
The lender charges interest on the balance, and the balance is highest at the start. In the example, $1,895.83 of the first $2,212.24 payment is interest. Each payment lowers the balance a little, so the next month's interest is smaller and more goes to principal.
When does principal overtake interest?
In the example it happens at payment 233, in the 20th year, when $1,107.99 goes to principal and $1,104.25 to interest. A lower rate or a shorter term moves that point earlier. Open the schedule to find it for your loan.
How much will I owe after 5 or 10 years?
Read the Balance column at payment 60 or payment 120. The example loan still owes $327,638.26 after 5 years and $296,716.04 after 10.
How do extra payments cut the interest I pay?
Each month's interest is the balance times the monthly rate. An extra payment goes straight to principal, so every month after it charges interest on a smaller balance. The regular payment stays the same, so more of each one goes to principal and the loan ends sooner. The months you no longer pay carry no interest at all. In the example, $200 extra a month saves 74 payments and $108,095.91 of interest. An extra paid early saves more than the same extra paid late, because it lowers the balance for more months. Starting from the balance you owe today? The mortgage payoff calculator takes the remaining balance and term.
Why is the last payment different from the others?
The calculator rounds the monthly payment to the cent, and each month's interest too. By the end of the term those roundings leave a small balance or a small overpayment. The last payment settles it: that month's interest plus whatever balance is left. In the example the last payment is $2,209.89, which is $2.35 less than the others. On a small loan over a long term, the rounded-up payment can clear the balance a month or more early, and the schedule then stops in that month.
Can I make a schedule at 0% interest?
Yes. Enter 0 as the rate. The payment is the loan amount divided by the months, rounded to the cent, and the last payment takes up the difference. $200,000 over 30 years at 0% is 359 payments of $555.56 and a last payment of $553.96, with no interest at all.