Mortgage Amortization Explained: How Your Payments Actually Work
What is amortization?
Amortization is the process of paying off a debt through regular, scheduled payments. Each mortgage payment covers two things: interest on the remaining balance, and a portion of the principal (the original amount borrowed). Over time, the balance shrinks to zero.
The key insight that surprises most homeowners: your payment amount stays the same, but the split between principal and interest shifts dramatically over the life of the loan.
How each payment is split
Each month, interest is calculated on your current balance. Whatever is left from your fixed payment goes to principal. Since the balance is highest at the start, early payments are mostly interest.
Here's a real example — $280,000 loan at 6.5% for 30 years (monthly P&I: $1,770):
| Payment | Principal | Interest | Remaining Balance |
|---|---|---|---|
| Month 1 | $253 | $1,517 | $279,747 |
| Month 12 | $268 | $1,502 | $276,827 |
| Month 60 (Year 5) | $346 | $1,424 | $262,632 |
| Month 120 (Year 10) | $474 | $1,296 | $238,436 |
| Month 240 (Year 20) | $887 | $883 | $161,284 |
| Month 300 (Year 25) | $1,213 | $557 | $100,928 |
| Month 360 (Year 30) | $1,761 | $10 | $0 |
Notice: it takes roughly 20 years before the principal portion exceeds the interest portion. In the first year alone, you'll pay about $18,000 in interest but only reduce your balance by about $3,200.
How to read an amortization schedule
An amortization schedule is a complete table showing every payment over the life of your loan. Each row includes:
- Payment number — Which month (1 through 360 for a 30-year loan)
- Payment amount — Your fixed monthly P&I payment
- Principal — How much of this payment reduces your balance
- Interest — How much goes to the lender as borrowing cost
- Remaining balance — Your outstanding loan amount after this payment
Our mortgage calculator generates a full interactive amortization schedule you can collapse by year and export as CSV.
The total cost of a 30-year mortgage
On a $280,000 loan at 6.5%, you'll pay $1,770/month for 360 months. That's $637,200 total — meaning you pay $357,200 in interest (more than the original loan amount).
This is why the interest rate matters so much. Here's how rates affect total cost on a $280,000 loan over 30 years:
| Interest Rate | Monthly P&I | Total Interest Paid | Total Cost |
|---|---|---|---|
| 5.0% | $1,503 | $261,084 | $541,084 |
| 6.0% | $1,679 | $324,328 | $604,328 |
| 6.5% | $1,770 | $357,200 | $637,200 |
| 7.0% | $1,863 | $390,528 | $670,528 |
| 8.0% | $2,054 | $459,434 | $739,434 |
A single percentage point difference (6% vs 7%) costs an extra $66,200 over the life of the loan.
15-year vs 30-year amortization
A 15-year mortgage has higher monthly payments but dramatically lower total interest. Comparing the same $280,000 loan:
| Term | Rate | Monthly P&I | Total Interest | Savings vs 30yr |
|---|---|---|---|---|
| 30 years | 6.50% | $1,770 | $357,200 | — |
| 15 years | 5.75% | $2,328 | $138,976 | $218,224 |
The 15-year mortgage costs $558/month more but saves over $218,000 in interest. That's a massive return on the extra monthly cost.
The power of extra payments
Making extra principal payments — even small ones — has an outsized impact because of how amortization works. Every extra dollar reduces the balance that future interest is calculated on.
Example: $100/month extra on a $280K loan at 6.5%
- Without extra: 30 years, $357,200 total interest
- With $100/month extra: 25.4 years, $289,710 total interest
- Saves: $67,490 in interest and 4.6 years of payments
Example: One extra payment per year
If you make one extra monthly payment each year (divide your payment by 12 and add that to each monthly check), you'll pay off a 30-year mortgage in roughly 25 years and save tens of thousands in interest.
When to make extra payments
Extra payments have the biggest impact early in the loan when interest charges are highest. An extra $100/month in year 1 saves far more than the same extra payment in year 25.
However, extra payments only make sense if:
- You have no high-interest debt (credit cards, personal loans)
- You have an adequate emergency fund (3-6 months expenses)
- You're maximizing employer retirement matching
- Your mortgage rate is higher than what you'd earn investing
Negative amortization: the danger
Some loan types (certain ARMs, payment-option mortgages) can have payments that don't cover all the interest due. The unpaid interest gets added to your balance — your loan actually grows over time. This is called negative amortization and should be avoided.
See your amortization schedule
Generate a complete month-by-month amortization schedule with our free mortgage calculator. Compare different loan terms and see exactly how extra payments accelerate your payoff.
Open Mortgage Calculator →Key takeaways
- Early mortgage payments are mostly interest — principal builds slowly at first
- On a 30-year loan, total interest often exceeds the original loan amount
- A 15-year mortgage saves hundreds of thousands in interest despite higher payments
- Extra principal payments have the biggest impact when made early
- Even small extra payments ($100/month) can shave years off your mortgage
- Always compare the total cost, not just the monthly payment