Mortgage Refinancing Math
Mortgage Basics
What Is a Mortgage?
Most people can't buy a house with cash. That's where a mortgage comes in. It's a loan from a bank or other financial institution that helps you purchase a home. Instead of paying the full price upfront, you borrow the money and pay it back over time.
A mortgage is a loan specifically designed for purchasing real estate, where the property serves as collateral.
The term “collateral” is key. It means if you stop making payments, the lender has the right to take the property. This arrangement protects the lender and makes it possible for them to offer large loans for long periods.
The Building Blocks of a Mortgage
Every mortgage is made up of a few core components. Understanding them is the first step to understanding your loan.
Principal
noun
The initial amount of money you borrow from the lender to buy the home. If you buy a $250,000 house and make a $50,000 down payment, your principal is $200,000.
Interest
noun
The fee the lender charges for letting you borrow their money. It's calculated as a percentage of the principal and is what makes lending profitable for the bank.
The principal and interest are the two main parts of your monthly payment. At the start of your loan, most of your payment goes toward interest. Over time, that shifts, and more of your money starts chipping away at the principal.
Term
noun
The length of time you have to repay the loan. Common mortgage terms are 15 years and 30 years. A shorter term means higher monthly payments but less total interest paid. A longer term lowers your monthly payment but means you pay more in interest over the life of the loan.
These pieces all come together in a process called amortization.
Amortization
noun
The process of paying off a loan with regular, fixed payments over a set period. Each payment covers both interest and a portion of the principal. An amortization schedule shows exactly how much of each payment goes to interest versus principal for the entire loan term.
Types of Mortgages
Not all mortgages are the same. The two most common types are fixed-rate and adjustable-rate. Your choice has a big impact on your monthly payment and overall cost.
Fixed-Rate Mortgage: The interest rate stays the same for the entire loan term. Your monthly principal and interest payment never changes. This predictability makes budgeting easy.
Adjustable-Rate Mortgage (ARM): The interest rate can change over time. It typically starts with a lower, fixed introductory rate for a few years, then adjusts periodically based on market conditions. Your monthly payment could go up or down after the initial period.
| Feature | Fixed-Rate Mortgage | Adjustable-Rate Mortgage (ARM) |
|---|---|---|
| Interest Rate | Stays the same | Changes after an initial period |
| Monthly Payment | Consistent and predictable | Can increase or decrease |
| Best For | Buyers who plan to stay in their home long-term and prefer stability. | Buyers who may sell before the rate adjusts or who are comfortable with potential payment changes. |
For example, a "5/1 ARM" means the interest rate is fixed for the first five years and then adjusts once every year after that. ARMs can be a good option if interest rates are high, as they offer a lower initial payment. However, they carry the risk that your payment could rise significantly in the future.
Let's check your understanding of these core concepts.
What is the primary purpose of a mortgage?
In a mortgage agreement, what does it mean for the property to serve as "collateral"?
Now you have a solid grasp of what a mortgage is and how it works. These fundamentals are the essential first step in the home-buying journey.