What is loan amortization?
Loan amortization is the process of gradually paying down a loan through a series of scheduled payments. Each payment generally contains two parts: interest and principal.
Interest is the cost of borrowing money. Principal is the portion of the payment that reduces the amount you still owe.
With many fixed-rate installment loans, the scheduled principal-and-interest payment remains the same each month, but the way that payment is divided changes over time.
Calculate interest
Interest is determined using the outstanding loan balance and the applicable periodic rate.
Apply the remainder
After interest is covered, the remaining part of the scheduled payment reduces principal.
Repeat with a lower balance
As principal falls, future interest generally decreases and principal repayment increases.
On a standard fixed-rate loan, the interest rate can remain unchanged while the interest portion of each payment decreases. The difference comes from the declining loan balance.
Why do early payments contain more interest?
At the beginning of a loan, the outstanding principal balance is at or near its highest point. Because interest is calculated using that larger balance, the interest charge is also relatively high.
As payments reduce principal, there is less unpaid balance on which to calculate future interest. That allows a larger share of the same scheduled payment to be applied to principal.
How the monthly payment is determined
For a standard fixed-rate amortizing loan, the payment is calculated so that the balance reaches zero after the scheduled number of payments, assuming payments are made as required and the loan terms do not change.
Example amortization calculation
Consider a $250,000 loan with a 6% fixed annual interest rate and a 30-year term.
The first month's interest is approximately $1,250 because 0.50% of the $250,000 balance is $1,250. The remaining approximately $248.88 of the payment reduces principal.
After that principal reduction, the next month's interest is calculated using a slightly smaller balance.
What is an amortization schedule?
An amortization schedule is a table showing how every scheduled payment affects the loan.
It typically includes:
- Payment number or date
- Scheduled payment
- Interest portion
- Principal portion
- Remaining balance
The schedule makes it possible to see exactly how repayment progresses rather than looking only at the monthly payment.
| Payment | Payment Amount | Interest | Principal | Remaining Balance |
|---|---|---|---|---|
| 1 | $1,498.88 | $1,250.00 | $248.88 | $249,751.12 |
| 2 | $1,498.88 | About $1,248.76 | About $250.12 | About $249,501.00 |
| 12 | $1,498.88 | About $1,235.96 | About $262.91 | About $246,929.97 |
See a full amortization schedule
Enter your own loan amount, rate and term to see how principal, interest and the remaining balance change throughout repayment.
Use the Amortization CalculatorHow mortgage amortization works
Most traditional fixed-rate mortgages are amortizing loans. The monthly principal-and-interest payment is structured so the mortgage balance reaches zero at the end of the scheduled term if all payments are made as required.
A 30-year mortgage usually has 360 scheduled monthly payments, while a 15-year mortgage usually has 180.
Property taxes, homeowners insurance, mortgage insurance and HOA fees are not part of the principal-and-interest amortization calculation even if some of those costs are collected with the monthly mortgage payment.
How auto loan amortization works
Many auto loans also follow an amortizing repayment structure. The borrower makes scheduled payments over a fixed term, and the balance gradually declines.
Because auto loans usually have shorter terms than mortgages, the balance can decline more quickly. Interest calculations and payment-processing practices can still differ by lender, so the specific loan agreement matters.
Personal loans and amortization
Fixed-rate personal installment loans commonly use amortization as well.
The borrower receives a principal amount and repays it over a predetermined number of scheduled payments. Each payment generally includes interest plus principal reduction.
How loan term affects amortization
A longer repayment term usually lowers the required monthly payment because the principal is spread across more payments.
However, keeping a balance outstanding for a longer period also creates more opportunities for interest to accrue.
A shorter term generally produces a higher monthly payment but allows principal to be repaid faster and can reduce the total amount of interest paid.
How interest rate affects amortization
A higher interest rate means a larger portion of a given payment may be needed to cover interest, especially early in the repayment schedule.
When comparing otherwise similar loans, a higher rate generally results in a higher scheduled payment, greater total interest or both.
What happens when you make extra principal payments?
An additional payment applied to principal reduces the outstanding balance ahead of schedule.
Because future interest is calculated using a smaller balance, extra principal payments can change the original amortization schedule, potentially reducing both payoff time and total interest.
The required payment may remain unchanged on many fixed-rate loans even though the balance reaches zero earlier.
What is negative amortization?
Normal amortization reduces the balance over time. Negative amortization is the opposite: the amount owed increases because the payment is not enough to cover the interest being added.
This does not occur with a standard fully amortizing fixed-payment loan when payments are made according to schedule, but it can occur with certain loan structures.
If a loan allows payments below the amount of accrued interest, unpaid interest may be added to the balance, causing principal owed to increase rather than decrease.
What is a balloon loan?
Not every loan is fully amortized by the end of the regular payment schedule.
Some loans are structured with smaller scheduled payments followed by a large remaining balance due at a specified time. That final amount is commonly called a balloon payment.
A balloon loan can therefore have an amortization schedule that does not reduce the principal to zero through the regular periodic payments alone.
Why an amortization schedule is useful
An amortization schedule can answer questions that a simple monthly payment figure cannot.
Why the payment can stay the same while the balance changes
One of the most confusing parts of amortization is that a fixed scheduled payment may remain unchanged even though the interest and principal portions are constantly changing.
Early in the loan:
- Outstanding principal is higher
- Interest charges are higher
- Less of the payment reduces principal
Later in the loan:
- Outstanding principal is lower
- Interest charges are lower
- More of the payment reduces principal
The payment itself can remain essentially the same while the internal allocation shifts from interest toward principal.
Your loan balance does not fall by the full payment amount
If your monthly payment is $1,500, the loan balance does not necessarily decline by $1,500.
First, the applicable interest for the period must be accounted for. Only the principal portion reduces the outstanding loan balance.
This is why a borrower may make thousands of dollars in payments during the first year of a long-term loan while seeing the balance decline by a much smaller amount.
Amortization gradually shifts a fixed loan payment from mostly interest toward increasingly more principal. As principal falls, interest generally falls too, allowing the balance to decline faster later in the repayment schedule.