Every mortgage comes with an amortization schedule — a month-by-month table showing exactly how each payment splits between interest and principal. Most borrowers never look at it. That's a mistake. The schedule reveals one uncomfortable truth: in the early years of a 30-year loan, the bank collects the lion's share of every payment you make.
How Amortization Works
Amortization means spreading loan repayment across equal periodic payments. Your monthly mortgage payment stays the same throughout the loan — but the interest/principal split changes dramatically over time.
Each month, your lender calculates interest on the remaining loan balance. In the early months, that balance is nearly the full loan amount, so interest is high. As you pay down principal, the balance drops, interest shrinks, and more of each fixed payment goes toward principal.
Monthly interest = Remaining balance × (Annual rate ÷ 12) Monthly principal = Fixed payment − Monthly interest Next month's balance = Current balance − Principal paid
A Concrete Example
On a $400,000 loan at 7% for 30 years, the monthly payment is $2,661. Here's how the first few payments break down:
| Month | Payment | Interest | Principal | Balance Remaining |
|---|---|---|---|---|
| 1 | $2,661 | $2,333 | $328 | $399,672 |
| 2 | $2,661 | $2,331 | $330 | $399,342 |
| 12 | $2,661 | $2,313 | $348 | $396,155 |
| 60 (yr 5) | $2,661 | $2,201 | $460 | $377,072 |
| 180 (yr 15) | $2,661 | $1,725 | $936 | $296,565 |
| 300 (yr 25) | $2,661 | $892 | $1,769 | $152,043 |
| 360 (yr 30) | $2,661 | $15 | $2,646 | $0 |
The Front-Loading Reality
In the first year, you pay $27,804 in total mortgage payments. Of that, $27,780 goes to interest and just $4,024 goes to principal — 87% interest, 13% principal. You own barely 1% more of your home after an entire year of payments.
By contrast, in year 29, that ratio flips: nearly all of each payment is principal. But most homeowners sell or refinance long before reaching that point.
When you refinance after 5 years, your amortization clock resets. You start a new 30-year schedule with a new loan — meaning your early payments are again mostly interest. Refinancing repeatedly can keep you in "mostly interest" territory for decades.
How to Use Amortization Knowledge to Your Advantage
- Make extra principal payments early: each dollar paid in year 1 eliminates ~$3–5 of total interest.
- Avoid restarting the clock: if refinancing, consider a 20- or 15-year term to maintain progress.
- Track your equity milestone: know exactly when you'll hit 20% equity to cancel PMI.
- Understand that selling early means most of your payments funded interest, not equity.
Reading Your Own Amortization Schedule
Your lender is required to provide an amortization schedule. But the most useful thing is an interactive version — where you can add extra payments and instantly see how they change your payoff date and total interest. That's what the Mortgage Calculator below does.
Amortization front-loads interest because lenders charge interest on the outstanding balance, which is largest at the start. Understanding this doesn't change how the math works — but it clarifies why early extra payments are so powerful and why repeatedly refinancing can be a trap. Pull up your own schedule, find your current principal balance, and calculate the impact of one extra payment per year.
