Updated June 17, 2026
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With an amortizing loan, every monthly payment is the same dollar amount, but the split between interest and principal shifts over time: early payments are weighted heavily toward interest, and later payments go mostly to principal, until the loan is paid off at the end of the term. This is how most personal loans, auto loans, and mortgages work.
How each payment is calculated
The lender uses your principal balance, annual interest rate, and number of payments to calculate a fixed monthly payment using a standard formula. Each month, interest is charged on the remaining balance. The rest of the payment reduces principal. Because the balance shrinks each month, the interest portion of the next payment is slightly smaller, and more goes to principal, and so on.
The formula itself is: monthly payment = P x [r(1+r)^n] / [(1+r)^n - 1], where P is the loan principal, r is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments. You do not need to memorize the formula; the loan calculator handles the arithmetic. But knowing the formula exists explains why payments are fixed while the internal split shifts each month.
A sample amortization schedule
| Month | Payment | Interest portion | Principal portion | Remaining balance |
| 1 | $386 | $117 | $269 | $19,731 |
| 6 | $386 | $110 | $276 | $18,099 |
| 12 | $386 | $101 | $285 | $16,341 |
| 24 | $386 | $82 | $304 | $12,592 |
| 48 | $386 | $29 | $357 | $4,183 |
| 60 | $386 | $2 | $384 | $0 |
This example uses a $20,000 loan at 7 percent over 60 months. Notice how the interest portion shrinks and the principal portion grows, while the payment stays constant. See the full schedule using the loan calculator.
Why you pay so much interest early
In the first year, the balance is at its highest, so interest charges are at their highest too. This is why paying off or refinancing a loan early in its life saves the most interest. If you sell a car or pay off a loan in month 12, you have repaid relatively little principal compared to the total payments made.
Here is a striking illustration. On a $300,000 30-year mortgage at 7 percent, the monthly payment is roughly $1,996. In month 1, about $1,750 of that goes to interest and only $246 reduces the principal. After one full year (12 payments totaling $23,952), the loan balance has dropped by only about $3,100. The remaining $20,800-plus in payments went entirely to interest. This front-loading effect is why paying extra early in a long mortgage produces disproportionate savings.
Is amortization just paying off a loan?
Technically, amortization refers to the specific schedule of payments that systematically reduces a loan to zero over a set period, with each payment covering both interest and principal. In casual use, people sometimes say "amortizing a debt" to mean paying it off generally, but the precise meaning is about the structured payment schedule. Not all debt repayment is amortization: a credit card, for example, is revolving debt with no fixed payoff schedule, so it does not amortize in the same sense.
How to use amortization to your advantage
Understanding amortization explains why extra principal payments are so powerful early in the loan. Every dollar of extra principal you pay in year one eliminates that dollar from the balance for all remaining months, saving interest across the full remaining term. See how to pay off a loan faster for strategies that use this to your advantage.
Types of loan amortization
- Fully amortizing: The standard type. Equal payments over the full term pay off both interest and principal so the balance reaches exactly zero on the last payment. Most personal loans, auto loans, and conventional mortgages use this structure.
- Negative amortization: Payments are less than the interest accruing, so the balance actually grows over time. Certain adjustable-rate mortgages and income-based student loan repayment plans can create negative amortization if the payment does not cover current interest.
- Balloon amortization: Payments are calculated using a long amortization period (such as 30 years) but the loan comes due in a short period (such as 5 or 10 years), leaving a large remaining balance called a balloon payment. Common in commercial real estate.
- Interest-only: Payments cover only interest for a set period, with no principal reduction during that phase. After the interest-only period, the loan either converts to a fully amortizing schedule or comes due in full.
What a 10-year loan amortized over 30 years means
This is a balloon structure sometimes seen in commercial real estate: payments are calculated as if the loan runs 30 years (keeping monthly payments low), but the loan term is only 10 years. At the end of year 10, the remaining balance (which is still large, since 30-year amortization is slow to reduce principal) is due in full as a balloon payment. Borrowers either pay it, sell the property, or refinance.
Disadvantages of amortization to know
Because so much interest is paid early, you build equity in a home or reduce a loan balance slowly at first. Selling or refinancing in the first few years means you have paid a lot in interest but still owe close to the original amount. It also means the total interest over a full loan term can be substantial, sometimes exceeding the original principal on long-term mortgages.
Amortization examples are for illustration and may not match your specific loan due to rounding, payment timing, or lender-specific terms. Not financial advice.
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