Determine Interest Over the Life of Your Mortgage

• 1). Determine your monthly payment, the number of payments that will be required to pay off the mortgage, and the original sales price for the property (principal balance). This information should be provided in your loan documentation or loan quote.
  
  
• 2). Multiply the monthly payment by the number of payments remaining on your mortgage (length of the loan). For example, if your monthly mortgage payment is $1,400 and you have 300 monthly payments remaining before the loan if paid in full, you should come up with the product of $420,000.
  
  
• 3). Subtract the principal or the original price of the property from the product that you determined in Step 2. For example, if you purchased your home for $350,000 you would subtract this amount from $420,000 (product of Step 2) and end up with $70,000. This is the amount that you would pay in interest over the life of your mortgage.
  
  

Determine Monthly Mortgage Interest

• 1). Determine the total remaining balance of your mortgage. The amount that you will pay in interest alone will vary from month to month, so when figuring out how much you are paying in interest for any one month, you need to know your current balance.
  
  
• 2). Multiply your current mortgage balance by your mortgage's interest rate. For example, if you had $250,000 left to pay on a mortgage that has a 6 percent interest rate, you should come up with $15,000. This is the amount that you will pay in interest for the year.
  
  
• 3). Divide your annual interest payment by 12 to determine how much your monthly mortgage payment will go toward interest. Drawing from the example, $15,000 divided by 12 would be $1,250 in interest for the month. Keep in mind that your principal will be less the next month and so on thereby causing your monthly interest payments to decrease over time.