Amortization Explained: How Loan Payments Work
Amortization is the process of spreading a loan into a series of fixed payments over time, where each payment covers both interest and principal. Early payments are mostly interest because the balance is highest; later payments are mostly principal. On a typical 30-year mortgage, you do not pay more principal than interest until around year 18 or 19. Understanding amortization helps you make smarter decisions about extra payments, refinancing, and loan terms.
Quick Answer
- *According to ConsumerAffairs, about 90% of mortgage holders choose a 30-year fixed-rate mortgage, the most common amortizing loan.
- *On a $400,000 mortgage at 6.5%, you will pay $510,177 in total interest over 30 years — more than the original loan amount.
- *Paying just $200 extra per month on that same mortgage saves approximately $107,000 in interest and pays it off 6 years early.
- *A 15-year mortgage at 5.85% on $400,000 costs $233,000 in total interest — saving $277,000 compared to a 30-year at 6.5%.
What Is Amortization?
When you take out a mortgage, auto loan, or personal loan, you agree to pay it back in equal monthly installments over a set term. Each payment has two components:
- Interest: The cost of borrowing, calculated on the remaining balance
- Principal: The portion that actually reduces your loan balance
Because interest is calculated on the outstanding balance, the interest portion is largest at the start (when the balance is highest) and smallest at the end. This is why a 30-year mortgage borrower pays mostly interest for the first decade.
How to Read an Amortization Schedule
Here is a simplified amortization schedule for a $400,000 mortgage at 6.5% over 30 years (monthly payment: $2,528):
| Payment | Total Payment | Interest | Principal | Remaining Balance |
|---|---|---|---|---|
| #1 | $2,528 | $2,167 | $361 | $399,639 |
| #12 (Year 1) | $2,528 | $2,144 | $384 | $395,522 |
| #60 (Year 5) | $2,528 | $2,010 | $518 | $381,166 |
| #120 (Year 10) | $2,528 | $1,800 | $728 | $352,183 |
| #216 (Year 18) | $2,528 | $1,266 | $1,262 | $233,878 |
| #240 (Year 20) | $2,528 | $1,128 | $1,400 | $207,118 |
| #360 (Year 30) | $2,528 | $14 | $2,514 | $0 |
Notice: In the first payment, only $361 of the $2,528 goes to principal — just 14.3%. After 5 years of payments ($151,680 total), you have only paid down $18,834 of the $400,000 balance. The crossover point — where principal exceeds interest — comes around payment #216 (year 18).
30-Year vs. 15-Year Mortgage: The Amortization Difference
| Factor | 30-Year at 6.5% | 15-Year at 5.85% |
|---|---|---|
| Loan amount | $400,000 | $400,000 |
| Monthly payment | $2,528 | $3,349 |
| Total interest paid | $510,177 | $202,820 |
| Total cost | $910,177 | $602,820 |
| Interest savings | — | $307,357 |
The 15-year mortgage costs $821 more per month but saves over $307,000 in interest. This is because you pay down the balance faster (less time for interest to compound) and typically get a lower rate.
How Extra Payments Accelerate Amortization
Extra payments go directly to principal, reducing the balance faster and cutting both the total interest and the loan term. Here is the impact on a $400,000 mortgage at 6.5% for 30 years:
| Strategy | Monthly Extra | Interest Saved | Years Saved |
|---|---|---|---|
| $100 extra/month | $100 | $62,000 | 3.5 years |
| $200 extra/month | $200 | $107,000 | 6 years |
| $500 extra/month | $500 | $196,000 | 11 years |
| 1 extra payment/year | ~$211 | $72,000 | 4.5 years |
The “one extra payment per year” strategy is popular because it is easy to implement: divide your monthly payment by 12 and add that amount to each monthly check (or make 26 bi-weekly payments instead of 12 monthly ones).
Amortization Beyond Mortgages
Auto Loans
Auto loans typically amortize over 3–7 years. According to Bankrate, the average auto loan rate was approximately 7.5% in late 2025. On a $35,000 car loan at 7.5% for 5 years, you would pay $7,092 in total interest with a monthly payment of $702.
Student Loans
Federal student loans use standard 10-year amortization, though income-driven repayment plans extend terms to 20–25 years. Unsubsidized loans accrue interest during school, which then capitalizes (gets added to the balance) at graduation — a form of negative amortization that increases the total cost.
Personal Loans
Personal loans typically amortize over 2–7 years. Because they are unsecured, rates are higher (8–15% for good credit), making the interest-heavy early payments particularly noticeable.
Negative Amortization: When Your Balance Grows
Negative amortization occurs when your payment does not cover the full interest charge, causing the unpaid interest to be added to the loan balance. This makes your balance increase over time rather than decrease. It can happen with:
- Adjustable-rate mortgages with payment caps
- Income-driven student loan repayment plans
- Some graduated payment mortgages
Negative amortization is dangerous because you can end up owing more than the original loan amount. Always check whether your payment fully covers the interest charge.
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Use our free Amortization Calculator →Also useful: Mortgage Calculator · 2026 Mortgage Rates Guide
Frequently Asked Questions
What is an amortization schedule?
An amortization schedule is a table showing every payment over the life of a loan, broken down into principal and interest portions. Early payments are mostly interest, while later payments are mostly principal. It shows you exactly how much of each payment reduces your loan balance.
Why do I pay so much interest at the beginning of my mortgage?
Interest is calculated on the remaining balance, which is highest at the start. On a $400,000 mortgage at 6.5%, the first payment includes $2,167 in interest and only $361 in principal. The crossover point where principal exceeds interest typically occurs around year 18–19 of a 30-year mortgage.
How much can I save by making extra payments on my mortgage?
On a $400,000 30-year mortgage at 6.5%, paying $200 extra per month saves approximately $107,000 in interest and pays off the loan 6 years early. One extra payment per year saves about $72,000 and cuts 4.5 years off the loan.