Mortgage Amortization: Why Early Payments Are Mostly Interest
On a 30-year mortgage, the payment stays the same but its makeup changes every month. Here is how amortization works, with a full example of where the money goes.
A fixed-rate mortgage payment is the same every month for 30 years. What changes is how each payment is split between interest and principal. In the early years, most of it is interest. By the end, almost all of it is principal. This shift is called amortization, and understanding it explains why extra payments early on are so powerful and why your balance seems to barely move for the first few years.
How each payment is split
Each month, interest is calculated on the remaining balance:
Because the balance is largest at the start, interest is largest at the start.
A worked example
A hypothetical $350,000 loan, 30-year fixed at 6.5%.
In the first month, about 86% of the payment goes to interest. Over the full 30 years, total interest comes to about $446,406, more than the original loan.
Show the numbers behind this chart
| Interest | Principal | |
|---|---|---|
| Year 1 | $22,635 | $3,912 |
| Year 5 | $21,477 | $5,070 |
| Year 10 | $19,536 | $7,011 |
| Year 15 | $16,852 | $9,695 |
| Year 20 | $13,141 | $13,406 |
| Year 25 | $8,008 | $18,538 |
| Year 30 | $912 | $25,635 |
Principal does not overtake interest within each payment until about month 233, nearly 20 years in.
How the balance falls
Show the numbers behind this chart
| Years into the loan | Remaining balance |
|---|---|
| Start | $350,000 |
| Yr 5 | $327,638 |
| Yr 10 | $296,716 |
| Yr 15 | $253,957 |
| Yr 20 | $194,828 |
| Yr 25 | $113,065 |
| Yr 30 | $0 |
After five years of payments, about $132,700 has been paid, but the balance has fallen by only about $22,400. Halfway through the term, at year 15, more than 70% of the original balance is still owed.
What this means in practice
Extra principal payments early have outsized effects. Every extra dollar paid toward principal stops interest on that dollar for the rest of the loan. Early in the loan, that is a long time. Our article on biweekly payments shows how one extra payment a year changes the timeline.
Equity builds slowly at first. If you sell after a few years, much of what you paid went to interest, and selling costs can exceed the equity built from payments alone. Price appreciation, not amortization, usually drives early equity.
Refinancing restarts the clock. A new 30-year loan begins again with interest-heavy payments, even at a lower rate. Comparing total remaining interest, not just the monthly payment, gives a clearer picture.
Shorter terms change the split. A 15-year loan has higher payments but a much larger share of each payment goes to principal from the start, and total interest is far lower.
Where to see your own schedule
Your lender's online portal or annual statement usually shows interest and principal paid. Any amortization calculator will produce a full schedule from your balance, rate, and remaining term.
The takeaway
The payment is fixed, but the split is not. Early payments are mostly interest, which is why extra principal early in the loan saves so much, and why refinancing into a new 30-year loan deserves a full comparison.
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