Amortization refers to the gradual repayment of a debt, usually a loan or a mortgage, through a series of regular payments over time. Each payment consists of both principal (the original amount borrowed) and interest (the cost of borrowing). As payments are made, the outstanding balance decreases. Amortization schedules typically show the distribution of each payment’s allocation to interest and principal, ensuring the debt is fully repaid by the end of the term.

Why is Amortization important?

Amortization is vital as it structures loan repayment, ensuring both principal and interest are gradually repaid. Amortization schedules provide borrowers with a clear understanding of how much they need to pay each period. This predictability aids in budgeting and financial planning. For assets like homes, amortization builds equity over time. As the principal balance decreases, the borrower’s ownership stake in the asset increases. Lenders, on the other hand, use amortization to ensure a steady stream of interest income and to mitigate their risk by gradually reducing the outstanding loan amount. Overall, amortization plays a crucial role in various financial transactions, aiding both borrowers and lenders in managing their financial obligations and making informed decisions.

How is Amortization calculated?

Amortization is calculated using a formula that takes into account the loan amount, interest rate, and the number of payments. The formula calculates the regular payment amount that includes both principal and interest.

The formula for calculating the monthly payment (PMT) for an amortizing loan is:

PMT = P * (r * (1 + r)^n) / ((1 + r)^n – 1)


PMT is the monthly payment

P is the principal loan amount

r is the monthly interest rate (expressed as a decimal)

n is the total number of payments.

Example of Amortization calculation

Let’s consider a simple example of a $10,000 loan with a 5% annual interest rate, to be repaid over 3 years (36 months) using monthly payments.

Step 1: Calculate the monthly interest rate

Monthly Interest Rate = Annual Interest Rate / 12

Monthly Interest Rate = 5% / 12 = 0.4167%

Step 2: Calculate the monthly payment using the formula for a loan payment:

Monthly Payment = P * (r * (1 + r)^n) / ((1 + r)^n – 1)


P = Principal amount ($10,000)

r = Monthly interest rate (0.4167%)

n = Total number of payments (36)

Monthly Payment = 10000 * (0.004167 * (1 + 0.004167)^36) / ((1 + 0.004167)^36 – 1)

Monthly Payment ≈ $299.71