CalcMortgage Amortization Calculator
Last updated: 2026-08-24
How to Use This Calculator
This mortgage amortization calculator is designed to help you understand the true cost of a loan by breaking down every payment into its principal and interest components. To use the calculator, simply enter the total loan amount (the amount you are borrowing), the annual interest rate offered by your lender, and the loan term in years. For example, a typical 30-year mortgage for $300,000 at 6.5% interest. Once you click 'Calculate', you will see your monthly payment amount, the total interest you will pay over the life of the loan, and the total cost (loan amount plus interest). Below that, a detailed amortization schedule shows each monthly payment: how much goes toward principal, how much toward interest, and the remaining balance after that payment. This schedule is especially useful for comparing different loan scenarios or planning extra principal payments to save on interest.
Formula and Methodology
The calculation uses the standard amortization formula for fixed-rate loans. The monthly payment (M) is calculated as: M = P × [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 (loan term in years multiplied by 12). For each payment period, the interest portion is the current balance multiplied by the monthly rate, and the principal portion is the monthly payment minus the interest. The balance is then reduced by the principal payment. This process repeats for each month, creating a full amortization schedule. The total interest is the sum of all interest payments, and the total cost is the sum of all payments.
Practical Examples
Example 1: A $200,000 loan at 5% annual interest for 15 years. Monthly payment = $1,581.59. Total interest = $84,685. Total cost = $284,685. After 5 years, you would have paid about $46,000 in interest and reduced the principal to around $149,000. Example 2: A $100,000 loan at 7% for 30 years. Monthly payment = $665.30. Total interest = $139,509. Total cost = $239,509. If you pay an extra $100 each month, you could save over $40,000 in interest and pay off the loan 8 years earlier. Use this calculator to experiment with different rates and terms to find the best option for your budget.
Tips and Best Practices
Always use the annual interest rate as provided by your lender, not the monthly rate. Remember that this calculator does not include property taxes, homeowners insurance, or private mortgage insurance (PMI) – those are additional costs that affect your total monthly payment. If you have an adjustable-rate mortgage (ARM), this calculator assumes a fixed rate for the entire term; actual payments may change when the rate adjusts. Consider making extra principal payments to reduce total interest and shorten the loan term. Review the amortization schedule to see the impact of extra payments. Finally, compare multiple lenders to find the best interest rate and terms before committing to a loan.
FAQ
What is amortization?
Amortization is the process of spreading out a loan into a series of fixed payments over time. Each payment covers both principal and interest, with the interest portion decreasing over the life of the loan.
Why does my interest payment change each month?
Interest is calculated on the remaining loan balance. As you pay down the principal, the balance decreases, so the interest portion of each payment also decreases, allowing more of your payment to go toward principal.
Can I use this for other types of loans?
Yes, this calculator works for any fixed-rate amortizing loan, such as auto loans, personal loans, or student loans. Just enter the loan amount, interest rate, and term.
What is the difference between total interest and total cost?
Total interest is the sum of all interest payments over the loan term. Total cost includes the original loan amount plus all interest, representing the full amount you will have paid by the end of the loan.