In the practice of real estate finance, there exist many different financing options. This article will evaluate the differences between a Constant Payment, Constant Amortization, and Interest Only payment type and their affect on cash flow and debt repayment. To illustrate these differences, let’s take a look at an example loan where the loan assumptions are found below:

For simplicity, let’s assume the term period and the amortization periods are the same; 25 years. The Constant Payment is calculated to fully amortize the loan over the 25 year period, the Constant Amortization is arrived at by dividing the beginning principal by the amortization period, and the Interest Only payment is assumed to pay the interest that accrues during the monthly compounding period. In the table below, we can compare the amount of interest paid over the life of the loan by payment type.

We can conclude that the Constant Amortization payment type requires the borrower to pay the least amount of interest over the life of the loan and that the Interest Only loan requires the borrower to pay the most amount of interest. Given this result, let’s examine how the principal is repaid for the three different payment types. The chart below details the debt balance for each year the principal remains outstanding.

From the Loan Balance chart, we can see that at any given year the loan balance for the Constant Amortization payment type is lower than the other payment types. With the Interest Only payment type loan, the entire principal balance remains outstanding throughout the life of the loan and is only repaid at the end of the term period. The Constant Payment type loan always maintains a higher outstanding principal balance as compared with the Constant Amortization type.
Finally, let’s examine the payment amounts for each loan type. The Constant Amortization loan repays with a fixed amount of principal plus interest accrued during the compounding period, therefore the payments are higher during the beginning of the loan as the principal balance is higher affecting the interest calculation. The chart below shows the amount of the payment for each type over time.

By definition the Constant Payment type does not change over time and remains at about $77,000. The Constant Amortization type starts at the beginning of the loan at about $99,000 and reduces to about $41,000 at the end of the loan. The Interest Only type remains at $60,000 until the end of the loan when the entire principal sum is repaid. While the Constant Amortization loan seems the most advantageous as it requires a lower total payment stream, it is weighted for higher payments at the beginning of the loan and lower payments at the end. The Interest Only type requires the lowest annual payment stream in the earlier years. You can see that at about year 18 the payment stream of the Constant Amortization payment type is about equivalent with the Interest Only payment type. After year 18, the Constant Amortization loan payments become the lowest. You can see at the end of the Interest Only loan the entire principal sum must be repaid all at once.
Another payment type we haven’t discussed here is the Graduated Payment. The Graduated Payment loan starts its life with a lower payment amount and it steps up once or more over the life of the loan. The most common form of a Graduated Payment loan is a loan that starts as an Interest Only payment for a period of time then switching to either a Constant Payment or Constant Amortization payment type.
Stabilized real estate Net Operating Income typically grows over time as rental rates rise. The most typical real estate loan is not conducive to a Constant Amortization loan as its payments are higher in the beginning and lower at the end while the real estate asset is better able to service the debt at the end then at the beginning. Lenders like Constant Amortization payment type because it returns principal faster reducing lender risk in a like fashion.
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