Interest Only Mortgage Calculator

  • Enter the Loan Principal, Interest Rate, Loan Term, and other details.
  • Choose the Interest Rate Type (Monthly or Annual).
  • Enter the Annual Property Tax and Annual Insurance if applicable.
  • Specify any Extra Monthly Payment you plan to make.
  • Check "Show Amortization Table" to display the full amortization table.
  • Click "Calculate" to compute the results.
  • Click "Clear Results" to reset the calculator.
  • Click "Copy Results" to copy the results to the clipboard.

The Interest Only Mortgage Calculator is a powerful financial tool designed to assist borrowers and investors in understanding the intricacies of interest-only mortgages. This tool provides valuable insights into the concept, calculations, benefits, and potential risks associated with this unique type of mortgage.

Concept and Purpose

Understanding Interest-Only Mortgages

An interest-only mortgage is a home loan in which the borrower only pays the interest on the principal amount for a specified period, ranging from five to ten years. During this period, the borrower is not required to make any payments towards the principal balance. This results in lower monthly payments compared to traditional amortizing mortgages. However, once the interest-only period expires, the borrower must start paying both principal and interest, leading to higher monthly payments.

The Role of the Calculator

The Interest Only Mortgage Calculator serves as a crucial tool for both prospective borrowers and investors. Its primary purpose is to provide clarity and transparency regarding the financial implications of an interest-only mortgage. Users can input relevant data, such as the loan amount, interest rate, and interest-only period, to obtain a comprehensive breakdown of their monthly payments and the total cost of the loan.


Monthly Interest Payment

The formula for calculating the monthly interest payment on an interest-only mortgage is straightforward:

Monthly Interest Payment = Loan Amount × (Annual Interest Rate / 12)

This formula calculates the interest portion of the monthly payment, which remains constant during the interest-only period.

Total Interest Paid

To determine the total interest paid over the life of the interest-only mortgage, the following formula is used:

Total Interest Paid = Monthly Interest Payment × Number of Months

This formula provides insight into the significant cost associated with interest-only mortgages, especially if the interest-only period is extended.

Monthly Principal Payment

After the interest-only period ends, borrowers need to pay down the principal. The formula for calculating the monthly principal payment during the amortization phase is:

Monthly Principal Payment = (Loan Amount / Number of Months Left)

This formula divides the remaining principal balance by the number of months left in the loan term.



Interest-only mortgages offer several benefits for both borrowers and investors:

Lower Initial Payments

One of the primary advantages of interest-only mortgages is that they provide borrowers with lower initial monthly payments. This can be particularly appealing for first-time homebuyers or real estate investors looking to improve cash flow.

Increased Affordability

Interest-only mortgages can make homeownership more accessible to a broader range of individuals, allowing them to enter the housing market with reduced financial strain.

Potential Investment Opportunity

Real estate investors use interest-only mortgages to finance property acquisitions. This strategy can optimize cash flow and potentially increase returns on investment properties.


Interest-only mortgages provide borrowers with flexibility in managing their finances. During the interest-only period, borrowers have the option to make additional principal payments if they choose to do so.

Risks and Considerations

While interest-only mortgages have their advantages, they also come with certain risks and considerations:

Balloon Payments

At the end of the interest-only period, borrowers face a significant increase in their monthly payments as they begin repaying both principal and interest. This “balloon payment” can be challenging for some borrowers to manage.

Potential for Negative Amortization

If the monthly interest payment does not cover the entire interest expense, the unpaid interest is added to the principal balance, leading to negative amortization. This means that the borrower owes more than the original loan amount, which can be financially detrimental.

Market Fluctuations

The success of an interest-only mortgage strategy relies heavily on the performance of the real estate market. A downturn in property values can leave borrowers underwater, owing more than their property is worth.

Interesting Facts

Historical Use

Interest-only mortgages were more prevalent before the 2008 financial crisis, contributing to the housing market bubble and subsequent crash. Today, they are less common and subject to stricter lending regulations.

Investor Strategies

Real estate investors use interest-only mortgages strategically to maximize their returns. By minimizing initial monthly payments, they can allocate more capital to other investment opportunities.


The Interest Only Mortgage Calculator is a valuable tool that sheds light on the complexities of interest-only mortgages. By providing users with the ability to calculate their monthly payments, total interest costs, and potential risks, this calculator empowers borrowers and investors to make informed decisions about their financial future.

While interest-only mortgages offer benefits such as lower initial payments and increased affordability, they also come with risks, including balloon payments and the potential for negative amortization. Therefore, individuals considering an interest-only mortgage should carefully weigh the pros and cons and seek professional financial advice when necessary.]

  1. Deng, Y., & Quigley, J. M. (2004). Mortgage terminations, heterogeneity, and the exercise of mortgage options. Econometrica, 72(5), 1377-1409.
  2. Glaeser, E. L., Gyourko, J., & Sinai, T. (2005). Urban growth and housing supply. Journal of Economic Geography, 5(2), 195-215.

Last Updated : 13 February, 2024

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