How To Calculate Interest on a Mortgage? | Tips for Home Buyers

How To Calculate Interest on a Mortgage?

06:37 AM September 13, 2019

Are you curious about how to calculate the interest on a mortgage? Understanding this important aspect can help you manage your finances better when buying a house.

Essentially, interest on a mortgage is the additional amount you pay for borrowing money to buy your home. This guide will break down the process of how interest is calculated on a mortgage.

Understanding Mortgage Interest

A mortgage loan is the most common way to finance expenses relating to education, weddings, or buying a home. Borrowers who do not have sufficient funds, loan the amount from a bank or mortgage lender. At the time of need, the lender pays for most of the equity – at times 80% of the cost of the new house. The borrower pays back in the form of a monthly payment with interest on the loan amount over a mutually decided period.

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The lender calculates monthly mortgage payments using the amortization formula. As per the agreement, the borrower pays back the principal and interest amount over the upcoming years. The life of the loan will decide how much a person is liable to pay monthly.

Loans can have fixed or adjustable interest rates. Lenders calculate Interest payments at a constant rate when you follow a fixed interest rate.

The amortization schedule outlines equal payments until the very last month when the borrower repays the total sum. An adjustable-rate mortgage monthly payment varies to account for changes in mortgage interest rates.

Planning for low monthly installments will result in a longer time for fully amortizing the loan amount. Under some circumstances, it can take more than 30 years. This is not attractive from a borrower’s point of view because it will require more interest payments depleting all savings.

How To Calculate Interest on a Mortgage?

Numbers with a question mark

As the name reflects, the interest accrued is the variable factor. Therefore, monthly payments are not the same throughout the longevity. The lender sets an upper and lower limit on how much the rate can fluctuate and its frequency. They calculate the payment amount by applying the current rate to the principal amount.

An increase in interest rate will cause monthly payments to increase. Most people prefer a lower rate in the initial few years, and higher in the final few years.

Sometimes the terms of mortgage loans mention a five-to-one-year adjustable rate. This means a fixed rate for 5 years and then the rate can change for the remaining loan balance.

The interest rate is determined by linking it to financial indexes such as inflation or yearly US treasury bills.

A $200,000 five to one-year adjustable-rate mortgage implies 4% interest for 5 years, after which the rate can change by 0.25% annually. The annual interest calculated for the starting five years amounts to $11,460 per year. It is is then divided by 12 to yield $955 per month. Increasing to $980 a month in the 6th year, and $1,005 in the 7th year of the loan.

How Mortgage Interest Works

Money and calculator to calculate mortgage interest

If you choose a 30-year fixed-rate mortgage plan, the monthly interest installments will remain constant. The borrower will pay a fixed amount every month until fully amortizing the loan.

Usually, such loans have a 30 years life. A borrower can also opt for shorter mortgage plans of 10,15 or 20 years. Shorter loan plans charge a lower interest rate, which minimizes the cost of the loan, but they result in higher monthly payments.

The annual interest rate of 4.5% is divided into 12 months will be 0.375% for every month. The borrower is liable to pay 0.375% of the principal amount loaned.

Now calculate the monthly payment for a $200,000 fixed interest rate mortgage at 4.5% will be around $1,013. The breakup of the monthly payment is $750 in interest and $263 is repayment of the principal amount.

Interest-only Loans

The next category of loans is interest-only loans. It works as an ideal scenario for buyers with unstable incomes.

The only obligation to pay is of interest till the first few years until the principal amount repayment. This kind of home financing facilitates low-income buyers as the monthly payment is low.

Those who do not plan to settle in a home for a long period can resale before bigger mortgage settlement payments set in.

Jumbo Loan

What if you set your eyes on a real estate that is a perfect match to your dream house? Prime location, big backyard, safe neighborhood for your children and so many more features.

But that home would cost you around half a million dollars- an amount that your bank balances cannot sum up to. What would you do?

While the Federal Housing Finance Agency does not authorize mortgage loans exceeding $453,100 all over the US excluding Hawaii, Alaska, and some other markets. Your only option for having the home for your family is through Jumbo Mortgage Loan.

Since the jumbo loan is not guaranteed by the state, it includes high risk for the lender.

In case of any losses, the lender will receive no compensation whatsoever from the state if the borrower goes bankrupt. To protect the lender, the application process and scrutiny of candidates have become stricter.

To qualify for a jumbo loan certain criteria must be met by the borrowers. Starting with, you must have a very high credit score. Credit scores reflect the creditworthiness of a borrower.

Handshaking while giving the house key after calculating the mortgage

Assessing Lender’s Risk and Strategies for Mortgage Loans

How much of a risk is involved from the lender’s perspective if it lends such a high sum of money to you? Ideally, a candidate with a score of 700-720 is a strong candidate.

Furthermore, lenders might have a look at your debt-to-income ratio. Most lenders will also assess your cash reserves. They expect you to be good enough to pay back one-year payments for existing reserves.

Prepare for additional expenses relating to escrow fees, taxes, and insurance while planning for mortgage loans.

Now that you understand how to calculate interest on a mortgage into payments are tax-deductible payments. A quick and successful method to gain complete ownership of your house is to pay additional money in each installment.

By paying extra each month depending on the ability, a borrower is likely to cover the principal amount earlier than expected. But this strategy is only advisable if all other loans such as credit card loans are paid and there is sufficient balance in the bank account.


Understanding how to calculate the interest on a mortgage is a crucial skill that can greatly benefit your financial management when purchasing a home. By grasping the concept of mortgage interest and its calculation process, you gain valuable insights into the financial dynamics of homeownership.

Remember, when it comes to mortgages, each borrower’s situation is unique, so it’s always beneficial to consult with professionals and explore personalized options based on your specific needs and circumstances.

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Frequently Asked Questions

What factors affect mortgage interest rates?

Several factors influence mortgage interest rates. The primary factors include the borrower’s credit score, the loan amount and term, the type of loan (fixed or adjustable rate), current market conditions, and the overall health of the economy. Lenders assess these factors to determine the level of risk involved in lending and adjust the interest rates accordingly.

Are mortgage interest rates the same for everyone?

No, mortgage interest rates can vary among borrowers. Lenders consider factors such as creditworthiness, debt-to-income ratio, loan-to-value ratio, and the type of mortgage being sought. Borrowers with stronger credit profiles and lower risk factors typically qualify for lower interest rates, while those with higher risk factors may face higher rates.

Can mortgage interest be tax-deductible?

In many cases, mortgage interest is tax-deductible. Depending on the jurisdiction and specific circumstances, homeowners may be able to deduct the interest paid on their mortgage from their taxable income. However, there are limitations and eligibility criteria that vary by country and region. It’s recommended to consult a tax professional or review the tax laws applicable to your situation for more information.

Published on September 13, 2019; Updated on June 23, 2023.

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