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

The principal payment for most mortgages changes monthly.

The principal payment for most mortgages changes monthly.

If you have a mortgage for which you pay both interest and principal every month, the amount you pay to each changes even if your payment remains the same. As your balance goes down, you owe less interest, which frees up more money to pay down your balance. Calculating the proportion of interest and principal payments can help you figure out how much closer you're getting to being mortgage free. It also lets you know how much interest you paid so you can estimate your mortgage interest tax deduction if you claim it.

Elements of a Mortgage Payment

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.

Amortization Tables

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.

Contacting Your Lender

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.


About the Author

Steve Lander has been a writer since 1996, with experience in the fields of financial services, real estate and technology. His work has appeared in trade publications such as the "Minnesota Real Estate Journal" and "Minnesota Multi-Housing Association Advocate." Lander holds a Bachelor of Arts in political science from Columbia University.

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