Every standard loan payment you make—whether it is a mortgage, a car loan, or a student loan—is divided into two distinct parts: Principal and Interest. Understanding the relationship between these two is the key to mastering debt.

The Principal

The principal is the actual money you borrowed. It is the core debt.

When you make a principal payment, you are returning the borrowed money to the lender. More importantly, making a principal payment directly increases your net worth (or equity). If you owe $100,000 on a house and pay $500 toward the principal, you now own $500 more of that house.

The goal of paying off a loan is to reduce the principal to $0.

The Interest

Interest is the fee the lender charges you for the privilege of using their money. It is the cost of borrowing.

When you make an interest payment, that money is gone forever. It is pure profit for the bank. It does not reduce your debt, and it does not build equity in your home.

The Relationship (Amortization)

The most important concept to grasp is that interest is always calculated as a percentage of the remaining principal.

Therefore, when the principal is high (at the beginning of a loan), the interest charge is high. When the principal is low (near the end of a loan), the interest charge is low.

In a standard fixed-rate mortgage, your total monthly payment never changes. To accommodate the shrinking interest charges, the balance shifts over time:

  • Year 1: Your payment is mostly Interest. Very little goes to Principal.
  • Year 15: Your payment is split roughly 50/50 between Principal and Interest.
  • Year 30: Your payment is mostly Principal. Very little goes to Interest.

The Lesson

Because interest is calculated based on the current principal, anything you can do to reduce the principal faster will result in less interest being charged.

If you have an extra $100 and you apply it as an "extra principal payment," the bank immediately lowers your core debt by $100. Next month, when they calculate your interest fee, they have to calculate it on a slightly smaller number. You have permanently reduced the bank's profit margin for the remainder of the loan.

See exactly how much you can save using our Mortgage Payoff Calculator.