What Is Amortization?
Amortization is the process of paying off a loan through a series of fixed, regular payments over a set period of time. Each payment covers the interest owed for that period plus a portion of the outstanding principal. Over the life of the loan, the balance gradually decreases until it reaches zero at the final payment.
How a Mortgage Amortizes
A standard fixed-rate mortgage is fully amortizing, meaning that if you make every scheduled payment on time, the loan will be paid off completely by the end of the term. The total monthly payment stays the same throughout the loan, but the split between interest and principal changes with every payment.
In the early years of a mortgage, the vast majority of each payment goes toward interest. This is because interest is calculated on the remaining loan balance — and in the beginning, that balance is at its highest. As you pay down the principal over time, less interest accrues each month, so more of each fixed payment goes toward reducing the balance.
The Amortization Formula
The monthly payment on a fixed-rate mortgage is calculated using the following formula:
Monthly Payment = P × [r(1+r)^n] / [(1+r)^n - 1]
Where:
P = Principal loan amount
r = Monthly interest rate (annual rate ÷ 12)
n = Total number of payments (loan term in years × 12)For example, on a $300,000 loan at 6.89% annual interest for 30 years:
- P = $300,000
- r = 6.89% ÷ 12 = 0.574167% per month (0.00574167)
- n = 30 × 12 = 360 payments
This produces a monthly principal and interest payment of approximately $1,975.
Sample Amortization Schedule
The table below shows the first five payments on a $300,000 loan at 6.89% for 30 years (monthly P&I payment: $1,975):
| Payment # | Monthly Payment | Interest Paid | Principal Paid | Remaining Balance |
|---|---|---|---|---|
| 1 | $1,975 | $1,723 | $252 | $299,748 |
| 2 | $1,975 | $1,721 | $254 | $299,494 |
| 3 | $1,975 | $1,720 | $255 | $299,239 |
| 4 | $1,975 | ~$1,718 | ~$257 | ~$298,982 |
| 5 | $1,975 | ~$1,716 | ~$259 | ~$298,723 |
Notice that in Payment 1, roughly 87% of the payment is interest and only 13% reduces the principal. This ratio gradually shifts over the decades, but the change is slow — after 10 years on this loan, a meaningful portion of each payment still goes to interest.
Why Front-Loading of Interest Matters
The front-loaded interest structure of an amortizing mortgage has an important implication: extra principal payments made early in the loan have an outsized impact. When you pay down extra principal, you reduce the balance on which future interest is calculated. That reduction compounds — each dollar of extra principal eliminates all the future interest that would have been charged on that dollar for the remaining loan term.
For example, making one extra $500 principal payment in month 12 of the loan above could eliminate several months of payments at the end of the 30-year term and save thousands of dollars in total interest. The earlier the extra payment, the greater the savings.
Types of Amortization Schedules
- Fully amortizing (standard): Equal payments over the full term; balance reaches zero at payoff. This is the most common structure for fixed-rate mortgages.
- Partially amortizing (balloon): Monthly payments are calculated as if the loan had a longer term (say, 30 years), but the remaining balance comes due as a lump sum after a shorter period (say, 5 or 7 years). Rare in consumer mortgages today.
- Interest-only: Monthly payments cover only interest for a set period; principal is not reduced until the interest-only period ends. Payments increase substantially when amortization begins.
- Negative amortization: Monthly payments are less than the interest owed, so unpaid interest is added to the principal balance. The balance grows over time rather than shrinking. These are uncommon and generally discouraged by regulators.
Amortization vs. Loan Term
The loan term (15-year, 20-year, 30-year) directly determines the amortization schedule. A shorter term means larger monthly payments but far less total interest paid over the life of the loan. A 15-year mortgage at the same rate as a 30-year will have a higher payment but will build equity much faster and cost significantly less in total interest.
You can model early payoff scenarios with the Mortgage Payoff Calculator. To understand how escrow is layered on top of principal and interest payments, see What Is Escrow?
Source: CFPB — What is an amortization schedule?
This definition is for informational purposes only and does not constitute financial advice.