How to Calculate Interest & Principal Applied to a Mortgage by the Date of Payments Made

Before calculating your interest and principal, you may need to strip extra items out of your mortgage payment. Some mortgage payments just include interest and principal, while others include principal, interest, taxes and insurance. If you don't know which type of payment you have, look at your statement. A mortgage with a PITI payment will show that you're funding your escrow account -- a repository for the money you pay toward taxes and insurance until these payments are sent to the insurer or tax collector. To find your real mortgage payment for the purpose of calculating principal and interest, look only at what you pay after subtracting the escrow. For instance, if your total payment is $1,750 and you pay $575 into your escrow account, your actual principal and interest payment is $1,175.

If you have it handy, look through your mortgage paperwork. Sometimes, lenders attach an amortization table or amortization schedule to the loan. The schedule lists all of your payments and, for each one, how much money goes to interest and how much goes to principal. You can look down the schedule, find the payment that corresponds to the date you're interested in and see how it is allocated.

Another way to calculate your interest and principal payment is to use a spreadsheet. The command for most spreadsheets for interest payments is IPMT and for principal is PPMT as of the date of publication. To use the command, you will need to know your loan's interest rate, the length of the loan, the amount you borrowed and which payment you're making. For instance, to find out the interest payment for the seventh payment on a 30-year, $150,000 mortgage at 5.25 percent, you would enter "=IPMT(5.25%/12,7,30*12,150000)," without the quotation marks, and then press the "Enter" key. The spreadsheet will calculate your interest payment of $651.68. You can calculate your principal payment of $176.62 by using the same command but with "PPMT" or by subtracting your interest payment from your total payment. You can change the numbers to fit your specific mortgage. Some spreadsheets, such as OpenOffice Calc, require you to use semicolons in place of commas in commands.

The easiest way to figure out your principal and interest payments might be to call your lender's customer service line. The lender can help you understand how much you pay to your principal and interest and how much, if anything, you pay toward other costs. It can also help you calculate the impact of paying extra on your mortgage if you'd like to get out of debt sooner.