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Amortization

Amortization is the process of paying off a loan through scheduled, equal payments that cover both principal and interest. Early payments are mostly interest; later payments are mostly principal.

Formula
M = P × r(1+r)ⁿ / ((1+r)ⁿ − 1)
Example

A $400,000 mortgage at 6.5% over 30 years has a monthly payment of $2,528. In month 1, $2,167 is interest and only $361 is principal.

An amortising loan (mortgage, car loan, personal loan) has a fixed payment schedule calculated so that the loan reaches a zero balance at the end of the term. Each payment is the same amount, but the split between interest and principal changes every period.

In the early years of a 30-year mortgage, the vast majority of each payment covers interest on the outstanding balance. As the principal shrinks, the interest portion falls and the principal portion rises — even though the monthly payment stays constant.

Lenders present this as an amortisation schedule: a table showing each payment, the interest paid, the principal paid, and the remaining balance. You can generate a full schedule with our mortgage calculator.

Put this into practice with our free calculator:

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Related terms

Principal
The principal is the original amount borrowed on a loan, or the outstanding balance still owed — excluding interest. On a mortgage, principal is the portion of each payment that reduces the loan balance.
Interest Rate
An interest rate is the percentage of the principal charged by a lender to a borrower for the use of money, or paid by a bank on deposited funds. It is quoted as an annual percentage.
Mortgage Payment
A mortgage payment is the fixed monthly amount owed to a lender, covering principal and interest (P&I). It may also include escrow for property tax and homeowners insurance (PITI).

Frequently asked questions

What is Amortization?
Amortization is the process of paying off a loan through scheduled, equal payments that cover both principal and interest. Early payments are mostly interest; later payments are mostly principal.
What is the Amortization formula?
The formula is: M = P × r(1+r)ⁿ / ((1+r)ⁿ − 1) — Example: A $400,000 mortgage at 6.5% over 30 years has a monthly payment of $2,528. In month 1, $2,167 is interest and only $361 is principal.