Cost Calculator AI
Real Estate & PropertyFixed-Rate Amortization

Mortgage Calculator

Calculate your monthly fixed-rate mortgage principal and interest payment, total lifetime interest, remaining balance, and payoff acceleration from optional extra monthly payments.

Mortgage Loan Details

Supports 0% interest loans as a valid case.

Fixed-Rate Amortization
Monthly Principal & Interest
$2,022.62

Loan Amount: $320,000.00 (20.0% Down)

Down Payment Amount$80,000.00
Total Interest Paid$408,142.36
Total Loan Payments (P + I)$728,142.36
Remaining Balance After Year 5$298,425.12
Interest Saved from Extra Payments$0.00 (0 mos saved)
Note: Calculates principal and interest (P&I). To include property tax, insurance, and PMI, see the Property Ownership Cost Calculator.

Standard Fixed-Rate Mortgage Amortization Formula

M = P ร— [r(1 + r)^n] / [(1 + r)^n โˆ’ 1] (or M = P / n when r = 0%)
  • P = Principal Loan Amount (Home Purchase Price minus Down Payment).
  • r = Monthly Interest Rate (Annual Interest Rate รท 100 รท 12).
  • n = Total Number of Monthly Payments (Loan Term in Years ร— 12).
  • Optional Extra Monthly Payment is applied directly to principal each month, reducing the remaining balance and shortening the payoff schedule.

Step-by-Step Worked Example

Scenario: Purchasing a $425,000 home with 20% down ($85,000) on a 30-year fixed mortgage at 6.5% interest

Calculation Steps:

  1. Monthly interest rate r = 0.065 รท 12 = 0.0054167
  2. Scheduled Monthly P&I = $340,000 ร— [0.0054167 ร— (1.0054167)^360] รท [(1.0054167)^360 โˆ’ 1] = $2,149.03/mo
  3. Total 30-year payments = $2,149.03 ร— 360 = $773,650.45 (Total Interest = $433,650.45)
Result: Your scheduled monthly principal and interest payment is $2,149.03, with $433,650.45 in total interest over 30 years.

How to Use This Calculator

  1. 1Enter the home purchase price.
  2. 2Choose whether to enter your down payment as a percentage or a dollar amount, then enter the value.
  3. 3Input your annual fixed mortgage interest rate and loan term in years.
  4. 4Optionally enter an extra monthly principal payment to see how much interest and time you can save.

Assumptions & Limitations

  • Assumes a standard fixed-rate, fully amortizing US mortgage compounded monthly.
  • Zero-interest (0% APR) loans are supported as a valid edge case where principal is divided evenly across all months.
  • Calculates principal and interest (P&I); use the Property Ownership Cost Calculator to include taxes, insurance, and HOA.

Frequently Asked Questions

Does this mortgage calculator include property taxes and homeowners insurance?

This calculator focuses on your core mortgage Principal and Interest (P&I) amortization and extra principal payments. To model full PITI + HOA + maintenance, use our Property Ownership Cost Calculator or Home Affordability Calculator.

How do extra monthly payments reduce total mortgage interest?

Because mortgage interest is calculated each month on the remaining principal balance, every extra dollar paid toward principal immediately lowers the balance that accrues interest in all subsequent months.

What happens if I enter a 0% interest rate?

For zero-interest loans (such as certain housing assistance or family loans), the calculator divides the loan principal evenly by the total number of monthly payments.

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