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Mortgage Interest: A Simple Guide to Saving on Your Home Loan

Shirel Berchowitz Updated: March 12, 2024 • 9 min read
man sitting in his garden in his home

Key Points:

  • Understanding mortgage interest is key when you're looking to buy a home.

  • Mortgage interest is the cost you pay to borrow money from a lender to purchase a home or other real estate.

  • This guide breaks down the basics of mortgage interest, including how it's calculated and what affects its rate, like the type of mortgage you choose (fixed, variable, or tracker) and other factors such as your loan amount and credit score.

Understanding mortgage interest is key when you're looking to buy a home. It's the extra money you pay on top of the loan you get from the bank to buy your house. This guide breaks down the basics of mortgage interest, including how it's calculated and what affects its rate, like the type of mortgage you choose (fixed, variable, or tracker) and other factors such as your loan amount and credit score. By getting to grips with these concepts, you'll be better prepared to choose the right mortgage, potentially saving money and reducing stress in the home-buying process.

What Is Mortgage Interest?

Mortgage interest is the cost you pay to borrow money from a lender to purchase a home or other real estate. It is essentially the fee charged by the lender for the use of its money. Mortgage interest is usually expressed as an annual percentage rate (APR), which can be fixed or variable depending on the terms of the mortgage.

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What Factors Affect the Amount of Interest You Pay?

The amount of interest you pay on a mortgage can be influenced by several key factors:

  • Interest Rate: The interest rate is the most direct factor affecting your interest payments. Higher rates result in higher interest costs over the life of the loan. Various factors including economic conditions, central bank policies, inflation, and the borrower's creditworthiness determine interest rates.
  • Loan Amount: The larger the loan amount (principal), the more interest you will pay. This is because interest is calculated as a percentage of the outstanding loan balance.
  • Loan Term: The length of your mortgage term affects your interest payments. Longer terms mean lower monthly payments but more total interest paid over the life of the loan, as you're borrowing money for a longer period. Shorter terms lead to higher monthly payments but less interest paid overall.
  • Type of Interest Rate (Fixed vs. Adjustable):
    • Fixed-rate mortgages lock in your interest rate for the duration of the loan, making your interest payments predictable.
    • Adjustable-rate mortgages (ARMs) have interest rates that can change over time based on market conditions. Initially, ARMs often offer lower rates than fixed-rate mortgages, but they can end up being more expensive if interest rates rise significantly.
  • Payment Frequency: The frequency of your mortgage payments can also impact the total interest paid. Making more frequent payments (e.g., bi-weekly instead of monthly) can reduce the amount of interest paid over the life of the loan by decreasing the principal balance more quickly.
  • Additional Payments: Making additional payments towards the principal balance of your mortgage can significantly reduce the total interest paid. This is because the interest is calculated on the remaining principal, which decreases with additional payments.
  • Credit Score: Borrowers with higher credit scores often qualify for lower interest rates because they are considered less risky to lenders. A lower interest rate means less interest paid over the life of the loan.
  • Loan-to-Value Ratio (LTV): This is the ratio of your loan amount to the property's value. A lower LTV ratio may qualify you for lower interest rates, indicating less risk to the lender.
  • Economic Factors: Broader economic conditions, such as inflation rates and the actions of central banks, can influence mortgage rates. For example, when the central bank raises its rates, mortgage rates tend to increase, affecting the interest you pay.

30-Year Fixed Rate Mortgage Average in the US

Source: FRED

How Is Mortgage Interest Calculated?

Mortgage interest is typically calculated using the simple interest formula, but the process involves a few steps due to the amortization of the loan. Amortization spreads a loan into a series of fixed payments over time. While the total payment amount remains the same throughout the loan term, the portion that goes towards interest decreases over time as the loan balance decreases.

Here's a basic overview of how mortgage interest is calculated:

1. Determine the Daily Interest Rate

First, you must convert the annual interest rate to a daily rate, as interest accrues daily. You do this by dividing the annual interest rate by the number of days in the year.

Daily Interest Rate=   Annual Interest Rate/365

(Note: Some lenders may use 360 days instead of 365 for calculations.)

2. Calculate Monthly Interest

To calculate the interest you'll pay in a particular month, multiply the daily interest rate by the current loan balance and then multiply that number by the number of days in the month.

Monthly Interest=Daily Interest Rate×Current Loan Balance×Days in Month

3. Amortization Calculation

Mortgage payments are typically fixed, meaning the total payment amount doesn't change over the life of the loan. However, the portion of each payment that goes towards interest versus principal changes over time. In the loan's early years, a larger portion of each payment goes towards interest. As the principal balance decreases, the interest portion of each payment decreases, and the principal portion increases.

An amortization schedule determines the exact distribution of interest and principal in each payment. This schedule is calculated at the beginning of the loan term and outlines how each payment is split.

Example Calculation

Let's say you have a $300,000 mortgage with a 30-year term and an annual interest rate of 4%.

  1. Annual Interest Rate to Daily Rate: 4%/365=0.000109589 =0.000109589 (approximately)
  2. Calculate Monthly Interest for the First Payment: Assuming 30 days in the month, the interest for the first month would be 0.000109589 \times 300,000 \times 30 = $986.30.

In the first payment, if the total monthly payment calculated by the amortization schedule is $1,432.25 (for example), then $986.30 goes towards interest, and the remainder ($445.95) goes towards reducing the principal. With each subsequent payment, the amount toward interest decreases, and the amount towards the principal increases.

Lenders use amortization formulas or calculators to calculate the exact distribution of payments for the entire loan term, which consider the total loan amount, the interest rate, and the loan term.

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How Does Mortgage Interest Work With Different Mortgage Types?

Mortgage interest works differently across various types of mortgages, primarily affecting how predictable your payments are over time and how much interest you might end up paying over the life of the loan. Here's how interest works with fixed-rate, variable-rate, and tracker-rate mortgages:

Fixed-rate Mortgage

  • How It Works: With a fixed-rate mortgage, the interest rate remains constant for the entire loan term. This means your monthly mortgage payments (principal and interest components) remain unchanged throughout the loan period.
  • Advantages: The predictability of payments makes budgeting easier for homeowners. You are protected from rising interest rates, which can increase the cost of borrowing.
  • Disadvantages: If interest rates fall, you might pay more in interest than variable-rate options unless you refinance your mortgage.

Variable-rate Mortgage (Also Known as Adjustable-rate Mortgage or ARM)

  • How It Works: Variable-rate mortgages have interest rates that can change over time. The initial interest rate is typically lower than that of fixed-rate mortgages but can fluctuate based on changes in market interest rates. These mortgages often have a fixed interest period at the beginning (e.g., 5 years at a fixed rate) and then adjust periodically.
  • Advantages: When market rates decline, you might benefit from lower interest rates (and lower payments). The initial lower interest rate can make these loans more affordable in the short term.
  • Disadvantages: Your monthly payments can increase if interest rates rise, making it harder to budget for mortgage payments. There's a higher level of uncertainty compared to fixed-rate mortgages.

Tracker-rate Mortgage

  • How It Works: Tracker-rate mortgages are a type of variable-rate mortgage where the interest rate directly tracks an external interest rate benchmark, usually the Bank Rate set by the central bank (e.g., the Bank of England's base rate), plus a fixed margin. For example, if the base rate is 1% and the lender adds a margin of 1%, your interest rate would be 2%.
  • Advantages: Transparency is key; your interest rate moves directly in line with the base rate, making it easier to understand why and how your payments change. If the base rate falls, your interest rate and monthly payments will decrease accordingly.
  • Disadvantages: Similar to other variable-rate mortgages, your payments can increase if the base rate increases. This can make budgeting challenging and increase the total amount of interest paid over the life of the loan if rates rise significantly.

Choosing the Right Type

The choice between these mortgage types depends on your financial situation, risk tolerance, and market conditions. Fixed-rate mortgages offer stability and predictability, making them suitable for those who prefer consistent payments. Variable-rate and tracker-rate mortgages might offer savings if interest rates fall but require a higher tolerance for risk and payment variability. It's important to consider your long-term financial goals and consult with a financial advisor or mortgage broker to choose the best mortgage type for your needs.

How Do Lenders Set Mortgage Interest Rates?

Lenders set mortgage interest rates based on a combination of factors that reflect the cost of lending, the risk associated with the loan, and broader economic conditions. Here's an overview of the main factors that influence how lenders set these rates:

1. Base or Benchmark Interest Rates

Lenders often start with a base or benchmark interest rate, such as the prime rate, the London Interbank Offered Rate (LIBOR, though less commonly used now), or government bond yields. These rates reflect the cost of borrowing money on the wholesale market or the interest rate at which banks lend to their most creditworthy customers. Changes in these base rates can influence the interest rates lenders charge for mortgages.

2. Central Bank Policy Rates

Central banks, such as the Federal Reserve in the United States or the European Central Bank in the Eurozone, set policy interest rates (e.g., the federal funds rate in the U.S.) that influence the cost of borrowing across the economy. These rates affect how much it costs banks to borrow money, influencing the rates they charge for loans, including mortgages.

3. Economic Conditions

Broader economic conditions, including inflation, economic growth, and the demand for mortgages, can also impact mortgage rates. For example, high inflation can lead to higher interest rates, as lenders must charge more to ensure their returns keep pace with rising prices.

4. Credit Risk

Lenders assess the risk that the borrower might not repay the loan. This risk assessment includes evaluating the borrower's credit score, income stability, debt-to-income ratio, and mortgage loan-to-value ratio. Borrowers deemed to be higher risk may be charged higher interest rates to compensate for the increased risk of default.

5. Loan Characteristics

The characteristics of the mortgage itself, including the loan amount, term (length of the loan), and whether the rate is fixed or adjustable, can affect the interest rate. For example, longer-term loans often have higher interest rates than shorter-term ones due to the increased risk of interest rate fluctuations.

6. Government Policies and Regulations

Government policies and regulations can also influence mortgage rates. For instance, government-backed mortgage programs might offer lower rates to promote homeownership among certain groups of borrowers. Additionally, regulatory changes affecting the banking and financial sectors can impact the cost of lending and, consequently, the interest rates charged.

7. Competition

Competition among lenders can play a significant role in setting mortgage rates. Lenders may adjust their rates to attract more customers or to remain competitive in the market, especially in environments where borrowers have many options.

Lenders use a combination of these factors to set their mortgage interest rates, aiming to balance the need to attract borrowers with the need to manage their risk and ensure profitability. Rates can vary significantly between lenders and over time, reflecting changes in these underlying factors.

Bottom Line

Mortgage interest is a critical component of the home-buying process, influencing both the monthly payments and the total amount paid over the life of a loan. By understanding these dynamics, borrowers can better navigate the mortgage market, choosing options that best fit their financial situation and goals. Whether prioritizing stability in monthly payments with a fixed-rate mortgage or taking advantage of potentially lower rates with variable or tracker-rate mortgages, informed decisions can lead to significant savings and a more manageable mortgage experience over time.



What is mortgage interest?

Mortgage interest is the cost you pay to borrow money from a lender to buy a home. It's essentially the fee charged for using the lender's money, expressed as a percentage of the loan.

What factors affect my mortgage interest rate?

Several factors can affect your mortgage interest rate, including your credit score, loan amount, down payment, loan term, and the current economic conditions. The type of mortgage (fixed, variable, or tracker) also plays a significant role.

How can I pay less interest on my mortgage?

You can pay less interest by making extra payments towards your mortgage principal, refinancing to a lower interest rate, or choosing a shorter loan term, which typically has lower rates.

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