How Loan Amortization Works (With a Worked Example)
Amortization is why your early mortgage payments are almost all interest. Here's the formula and what it means for paying off a loan.
What amortization means
Amortization is the process of paying off a loan with equal periodic payments, where each payment covers the interest due plus a bit of principal. Because interest is charged on the outstanding balance, and the balance is highest at the start, your early payments are mostly interest and your later payments are mostly principal.
The monthly payment on a fixed-rate loan is set by the amortization formula: M = P · r(1+r)n / ((1+r)n − 1), where P is the loan amount, r is the monthly interest rate (the annual rate divided by 12), and n is the total number of monthly payments.
A worked example
Take a $300,000 loan at 6.5% for 30 years. The monthly rate is 6.5% ÷ 12 = 0.5417%, and there are 360 payments. Plugging into the formula gives a monthly payment of about $1,896.
In month one, interest is $300,000 × 0.5417% = $1,625, so only about $271 goes to principal. By the final year, almost the entire payment reduces principal. Over the full loan you pay roughly $382,600 in interest — more than the amount you borrowed. Generate the full table with the amortization schedule calculator.
Why this matters for payoff strategy
Because so much early interest rides on the balance, paying extra principal early saves dramatically more than the same amount paid later — each early dollar erases years of future interest on that dollar. That's the logic behind extra-payment strategies.
It also explains why stretching a loan to a longer term, while lowering the payment, raises total interest: more months means more interest accrues before the balance is gone.
Run your numbers
Try the Amortization Schedule Calculator to see how this applies to your own situation.
Open the Amortization Schedule Calculator →Frequently asked questions
Why is most of my mortgage payment interest at first?
What is the amortization formula?
Informational only — not financial or tax advice. This article is general educational information and may not reflect current figures or your individual situation. Tax and financial rules change; verify with the IRS or a qualified professional before acting.