Mortgage Amortization Explained: How Your Loan Balance Changes

When you take out a standard 30-year fixed-rate mortgage, you agree to make the exact same monthly payment every month for 360 months. However, what that payment actually pays for changes dramatically between month 1 and month 360.

This shifting balance between paying off your debt and paying the bank's fee is called amortization.

What is Amortization?

Amortization is the process of spreading out a loan into a series of fixed payments over time. While the total payment remains equal each period, the proportion of the payment that goes toward the principal (the actual loan amount) and the interest (the cost of borrowing) changes.

The Early Years: Paying for Time

Interest on a mortgage is calculated based on your current outstanding balance. In the very first month of your loan, your balance is at its absolute highest. Therefore, the interest charged for that month is also at its highest.

Because your total monthly payment is fixed, and the interest charge is huge, only a tiny sliver of your payment actually goes toward paying down the principal.

For example, on a $300,000 loan at 6.5% interest, your first month's Principal & Interest payment is $1,896. Of that, $1,625 goes to the bank as interest, and only $271 goes toward your principal!

The Tipping Point

As you slowly pay down that principal—even by just $271 in the first month—your balance for the second month is slightly lower ($299,729). Therefore, the interest calculation for the second month is slightly lower.

Because the total payment is still $1,896, but the interest charge dropped by a few dollars, a few more dollars go toward the principal in month two.

This creates a compounding effect. Every month, the interest charge drops, and the principal payment grows. About halfway through a 30-year loan, you reach the tipping point where more of your monthly payment goes toward principal than interest.

Amortization Schedules

An amortization schedule is a complete table of periodic loan payments, showing the amount of principal and the amount of interest that comprise each payment until the loan is paid off at the end of its term.

The Power of Extra Payments

Understanding amortization reveals a powerful financial hack. If you make an extra payment, 100% of that extra money goes directly toward the principal.

By artificially lowering your principal balance today, you permanently lower the interest calculations for every single month remaining on the loan. This is why making even small extra payments early in the loan can shave years off your term and save tens of thousands of dollars.

Explore this math yourself using our Mortgage Payoff Calculator.