How Loan Amortization Works (With a Real Example)
Loan amortization is the schedule that shows how each payment on a fixed-rate loan is split between interest and principal. Understanding it helps you compare loans, plan extra payments and see the real cost of borrowing. Below we explain the formula, walk through a real $200,000 example and show how the term changes the total you pay.
- A fixed payment is split between interest and principal, and the split changes every month.
- Early payments are mostly interest, so equity builds slowly at first.
- A shorter term costs more per month but far less in total interest.
What is loan amortization?
Amortization comes from an old word meaning "to kill off": the debt is gradually killed off through regular payments. With a standard fixed-rate loan, you make the same payment every month. That payment is split into two parts: interest, which is the lender's charge for the money you still owe, and principal, which reduces the balance itself.
The payment stays constant, but the split does not. Early on, the balance is large, so most of the payment covers interest. Over time the balance shrinks, interest falls, and a bigger share of each payment goes to principal. This shifting mix is the single most important idea for understanding any installment loan, whether it is a mortgage, an auto loan, a personal loan or a student loan.
The amortization formula
The monthly payment on a fixed-rate loan is calculated with this standard formula:
M = P × r × (1 + r)n ÷ ((1 + r)n − 1)
- M is the monthly payment.
- P is the amount you borrow (the principal).
- r is the monthly interest rate, which is the annual rate divided by 12.
- n is the total number of monthly payments, such as 360 for a 30-year loan.
You never need to do this by hand, because the Ledgercal loan calculator applies the same formula instantly. But knowing it explains why a small change in rate or term moves the payment so much: both sit inside the exponent.
A worked example: $200,000 at 6% for 30 years
Using the formula, the monthly payment is $1,199.10. In month one, interest is $200,000 × 0.5% = $1,000.00, so only $199.10 reduces the principal. The table shows how the split changes over the life of the loan.
| Month | Payment | Interest | Principal | Balance after |
|---|---|---|---|---|
| 1 | $1,199.10 | $1,000.00 | $199.10 | $199,801 |
| 2 | $1,199.10 | $999.00 | $200.10 | $199,601 |
| 3 | $1,199.10 | $998.00 | $201.10 | $199,400 |
| 60 | $1,199.10 | $931.88 | $267.22 | $186,109 |
| 120 | $1,199.10 | $838.66 | $360.44 | $167,371 |
| 240 | $1,199.10 | $543.31 | $655.79 | $108,007 |
| 360 | $1,199.10 | $5.97 | $1,193.14 | $0 |
Notice how the interest share falls: it is about 83% of the payment in month one, about 45% in month 240, and only pennies on the dollar near the end.
Why early payments are mostly interest
Interest is charged on the balance that is outstanding at the time, not on the original amount. On day one you owe the full $200,000, so interest is at its peak. In the first year of this loan you pay about $11,933 in interest out of $14,389 in total payments.
The effect is slow equity building. After five years (60 payments) the balance is still about $186,109, and after ten years it is about $167,371. In other words, you have repaid only around 16% of the principal after one third of the term. This is normal, but it is also why early extra payments are so powerful and why refinancing late in a loan rarely saves as much as many people expect.
How the term changes the total cost
A shorter term raises the payment but removes years of interest. Same loan, same 6% rate:
| Term | Monthly payment | Total interest | Total repaid |
|---|---|---|---|
| 15 years | $1,687.71 | $103,788 | $303,788 |
| 25 years | $1,288.60 | $186,581 | $386,581 |
| 30 years | $1,199.10 | $231,676 | $431,676 |
| 35 years | $1,140.38 | $278,959 | $478,959 |
Moving from 30 to 15 years raises the payment by about $489 a month but cuts total interest by roughly $127,888. A longer term feels cheaper each month yet costs far more overall, so choose the shortest term your budget can comfortably carry.
How to read an amortization schedule
An amortization schedule lists every payment with four columns: the payment number, how much goes to interest, how much goes to principal, and the remaining balance. Three things are worth checking:
- The crossover point, where principal first exceeds interest. On this loan it happens in month 223, more than 18 years in.
- The balance at key dates, such as the year you might sell, refinance or move.
- The total interest, which is the sum of the interest column and the real price of borrowing.
You can generate a full schedule for your own numbers in the calculator, and export it as a CSV file to open in a spreadsheet.
What can change the schedule
Anything that lowers the balance sooner rewrites the schedule in your favor. Extra principal payments, a larger down payment, a lower rate through refinancing and a shorter term all reduce total interest. Our guide on extra loan payments shows exactly how much, and the article on lowering your monthly payment explains the trade-offs of the other options.
Keep in mind that this article covers fixed-rate loans. If your rate can change, the schedule is recalculated at each adjustment, as explained in fixed vs variable rate loans.
Frequently asked questions
Is amortization the same as depreciation?
No. Amortization here means paying down a debt over time. Accountants also use the word for spreading the cost of an intangible asset, but that is a different concept.
Do I pay the same interest every month?
No. The payment is constant, but the interest portion falls each month because it is calculated on a shrinking balance.
Can a loan have no amortization?
Yes. Interest-only and balloon loans do not reduce principal during part or all of the term, so a large amount may be due at the end. Check your loan agreement carefully.
Keep reading
- Should You Make Extra Loan Payments? How Much You Can Save
- Fixed vs Variable Rate Loans: Which Is Better?