Understanding Loan Amortization: Schedule, Formula, and Examples

What Is Amortization?

Amortization is the process of paying off a loan with regular payments so that the amount you owe decreases with each payment. In a typical amortizing loan, a portion of each payment goes toward the principal (the amount you borrowed) and a portion goes toward the interest (the cost of borrowing).

With a fixed-rate amortizing loan, your combined principal-and-interest payment stays the same for the life of the loan, but the split between principal and interest changes. Early on, a larger share goes to interest because the outstanding balance is larger. As you pay down the balance, the interest portion shrinks and more of your payment goes to principal.

Amortization is distinct from negative amortization, which can occur when a payment is not enough to cover the interest due, causing the unpaid interest to be added to the principal and increasing the amount you owe.

• At the start of the loan, most of each payment is applied to interest rather than principal.
• The principal balance decreases slowly at first, then more quickly near the end of the term.
• A longer loan term means lower monthly payments, but you pay more total interest over the life of the loan.

Sources: Consumer Financial Protection Bureau

The Amortization Formula

The standard amortization formula calculates the fixed monthly payment required to pay off a loan over a specified term at a given interest rate. In plain notation, the monthly payment (M) is:

M = P × [ r(1 + r)^n ] / [ (1 + r)^n – 1 ]

where P is the principal or loan amount, r is the monthly interest rate (annual rate divided by 12, expressed as a decimal), and n is the total number of monthly payments (loan term in years multiplied by 12).

The interest portion of each payment is calculated based on the current outstanding principal balance. Multiply the monthly interest rate by the remaining balance to find the interest for that period. The rest of the payment reduces the principal. This is how lenders typically handle interest on amortizing loans.

• Lenders may calculate interest daily or monthly, but the result is based on the actual outstanding balance each period.
• Because the balance decreases over time, the interest portion of each payment also decreases.

Sources: Consumer Financial Protection Bureau

Sample Amortization Schedule for a $200,000 Loan

To see how amortization works in practice, consider a $200,000 loan with a 6% annual interest rate and a 30-year term. Using the amortization formula, the monthly payment is approximately $1,199.10. The table below shows the first few payments and the final payment, illustrating how the interest portion decreases over time.

Note that in an amortizing loan, the interest portion of each payment is calculated based on the outstanding principal balance at that time. Because the balance decreases slowly at first, the interest portion remains high in the early years.

In this example, the interest portion drops from about $1,000 in the first payment to just over $5 in the final payment. The final payment is adjusted to account for rounding across the life of the loan; federal rules allow lenders to adjust the last payment to fully amortize the loan when rounding creates a small difference.

Sources: Consumer Financial Protection Bureau

How Principal and Interest Split Changes Over Time

In the early years of a 30-year loan, most of each payment goes to interest. The balance declines only slightly with each payment, so the interest—which is a percentage of that balance—remains high. As the balance drops, the interest portion falls and the principal portion grows.

The crossover point—when the principal portion first exceeds the interest portion—depends on the interest rate and term. For a higher rate or a longer term, the crossover happens later; for a lower rate or shorter term, it happens sooner.

This pattern matters because it affects how quickly you build equity in a home or how fast you own a car outright. It also explains why paying extra early in the loan can significantly reduce total interest.

• The interest portion is based on the outstanding principal balance at that time.
• The principal portion increases over time, while the interest portion decreases.
• The combined payment remains the same for a fixed-rate loan.

Sources: Consumer Financial Protection Bureau

Extra Payments on Amortization

Making an extra payment toward principal reduces the outstanding balance immediately. Since interest is calculated on the remaining balance, a lower balance means less interest accrues in future periods. If you continue making your regular monthly payment, the extra principal payments shorten the overall loan term and reduce total interest paid.

The exact savings depend on the loan terms, which can vary.

Keep in mind that some loans may have prepayment penalties or restrictions, so it's wise to check your loan documents or ask your lender. But for most standard amortizing loans, extra principal payments are allowed and can be a powerful way to reduce your total cost.

• Extra payments reduce the principal balance, leading to a shorter loan term and less total interest paid.
• The effect is strongest early in the loan when the balance is highest.
• Check your loan agreement for any prepayment penalties or rules.

Sources: Consumer Financial Protection Bureau

Amortization vs. Simple Interest Loans

Many amortizing loans use a simple interest structure, meaning interest is charged on the actual outstanding balance each period. This is the type of loan described throughout this guide.

Some loans, however, use precomputed interest. In a precomputed interest loan, the lender adds the total interest to the principal at the start, and your payments are applied to that combined amount. If you pay early or make extra payments, you may not reduce the interest owed because the interest was already calculated and built into the loan.

The distinction matters when you consider prepayment. With an amortizing loan, extra payments reduce both the balance and the interest you pay. With a precomputed loan, making extra payments in the middle of the loan may not reduce the total interest that was already charged.

Some loans have balloon payments, where a final payment is much larger than the regular payments. Balloon payments do not fully pay down the loan over the regular payment schedule.

• Many amortizing loans use simple interest calculations, but not all simple interest loans are amortizing.
• Precomputed interest loans add total interest upfront; extra payments may not reduce interest.
• Balloon payments can require a large final payment, which affects the amortization schedule.

Sources: Consumer Financial Protection Bureau

How to Create Your Own Amortization Schedule

You can build an amortization schedule yourself using a spreadsheet or a pen and paper. Start with the loan amount, the annual interest rate, and the loan term in years. Convert the annual rate to a monthly rate by dividing by 12, and find the total number of payments by multiplying the years by 12.

To calculate the monthly payment, use the amortization formula from earlier in this guide. If you prefer not to use the formula, many loan payment calculators and spreadsheet functions (such as the PMT function in Excel or Google Sheets) can do the math for you.

Once you have the payment, set up a table with columns for payment number, payment amount, interest portion, principal portion, and remaining balance. For each row, calculate the interest as the monthly rate times the previous balance, then subtract that interest from the payment to get the principal portion. Subtract the principal portion from the previous balance to get the new balance.

Because of rounding, the final payment may need to be slightly adjusted to bring the balance to zero. Federal rules for mortgage disclosures permit lenders to ignore minor rounding differences and adjust the last payment accordingly.

You can also add an extra principal column if you plan to make additional payments. Simply subtract the extra amount from the balance after the regular principal portion, and continue the schedule with the lower balance.

• Use the formula: M = P × [ r(1 + r)^n ] / [ (1 + r)^n – 1 ]
• Create columns for payment number, payment amount, interest, principal, and balance.
• Calculate interest based on the outstanding balance at the start of each period.
• Adjust the last payment for rounding, if needed.

Sources: Consumer Financial Protection Bureau