Mortgage Amortization, Explained
Why early payments are mostly interest, how the split shifts over time, and how extra payments attack the balance.
Amortization spreads a loan into equal monthly payments, but the split changes every month: early payments are mostly interest, later payments are mostly principal. On a $320,000 loan at 6.5 percent for 30 years, month one sends about $1,733 to interest and $290 to principal; by year 15 the split is roughly even.
What amortization means
Amortization is the process of paying off a loan in fixed installments. Each monthly payment covers that month's interest first, and whatever is left reduces the principal. Because interest is charged on the remaining balance, the interest slice shrinks a little every month and the principal slice grows.
The payment itself never changes on a fixed-rate loan. What changes is the internal split. That is why a payoff schedule is front-loaded with interest even though every check you write is the same size.
The split, month by month
On a $320,000 loan at 6.5 percent for 30 years, the payment is about $2,023. Month one: about $1,733 interest, $290 principal. Month 60 (year five): about $1,610 interest, $413 principal. Month 180 (year 15): about $1,280 interest, $743 principal. The crossover, where principal finally exceeds interest, arrives around year 19.
This is why refinancing restarts the clock in a costly way. A new 30-year loan puts you back at the interest-heavy end of the schedule, even if the rate is lower. Always compare total interest, not just the monthly payment.
How extra payments help
An extra principal payment skips the interest queue entirely: every extra dollar reduces the balance that future interest is charged on. Adding $200 a month to the example loan above cuts roughly 7 years off the term and saves on the order of $130,000 in interest.
One extra payment a year, often done by switching to biweekly half-payments, has a similar effect: it is the equivalent of about one extra monthly payment annually, shaving roughly 4 to 5 years off a 30-year loan.
Reading an amortization schedule
A schedule lists every payment with its date, interest portion, principal portion, and remaining balance. Scan the balance column to see when you cross equity milestones: 20 percent equity (PMI removal on conventional loans), or the point where selling would clear the loan after costs.
If you are comparing loan offers, line up the total interest rows. Two loans with the same rate but different fees, or the same payment but different terms, tell very different stories in the total-interest column.
Skip the arithmetic
Run your own loan through the free mortgage calculator to see the payment, total interest, and lifetime cost.
Amortization questions
Why is my first mortgage payment almost all interest?
Because interest each month is charged on the outstanding balance, and the balance is at its largest on day one. On a $320,000 loan at 6.5 percent, the first month's interest alone is about $1,733 of the $2,023 payment, leaving only $290 for principal. The split shifts a little toward principal every month.
Do extra mortgage payments really save that much?
Yes, because extra principal payments skip the interest queue: each extra dollar reduces the balance that all future interest is calculated on. An extra $200 a month on a typical 30-year loan can shave years off the term and save well over $100,000 in interest, with the biggest savings coming from extra payments made early.
What is negative amortization?
Negative amortization happens when the monthly payment is smaller than the interest due, so the unpaid interest gets added to the loan balance and the debt grows instead of shrinking. It is rare in standard fixed-rate mortgages but can appear in some adjustable or minimum-payment loan structures.