Most first-time US homebuyers are surprised by their first mortgage statement. They pay $2,500 and the loan balance drops by only a few hundred dollars. Nothing is wrong. That's amortization, and once you understand it you can make better choices about loan terms, down payments and extra payments.
What amortization means
An amortizing loan has a fixed principal-and-interest payment that pays off the debt over a set term, usually 15 or 30 years. The payment stays the same, but the split between interest and principal changes every month:
- Interest is charged on the remaining balance, so it's highest at the start.
- Principal is whatever is left of the payment after interest, so it starts small and grows.
The payment formula
M = P × [r(1 + r)^n] ÷ [(1 + r)^n − 1]
- P = loan amount
- r = monthly interest rate (annual rate ÷ 12)
- n = number of payments (years × 12)
Example: a $320,000 loan at 6.75% for 30 years.
- r = 0.0675 ÷ 12 = 0.005625, and n = 360
- M ≈ $2,075.51 for principal and interest
Month 1 vs month 240
Month 1: interest = $320,000 × 0.005625 = $1,800.00, so principal = $2,075.51 − $1,800 = $275.51. About 87% of that first payment is interest.
By month 240 (year 20), the balance is around $181,000. Interest is about $1,020, and roughly $1,055 goes to principal. The payment is the same, but the split has flipped.
Over the full 30 years you'd pay about $427,000 in interest, more than the original loan. A mortgage amortization calculator shows this month by month and lets you see how the schedule changes when you add extra payments.
PITI: the full monthly payment
Lenders and real estate agents usually quote PITI, not just principal and interest:
| Piece | What it is | Example (monthly) |
|---|---|---|
| Principal | Pays down the loan | $275 (month 1) |
| Interest | Lender's charge | $1,800 (month 1) |
| Taxes | Property tax, held in escrow | $400 |
| Insurance | Homeowners insurance, held in escrow | $150 |
| Total | ≈ $2,625 |
Taxes and insurance go into an escrow account that your servicer uses to pay those bills for you. They aren't part of the amortization schedule, and they can go up every year. That's why payments on a "fixed-rate" mortgage can still increase. If your county reassesses your home and the tax bill jumps, your escrow payment jumps too.
HOA dues are usually paid separately, but lenders count them when deciding how much you can afford.
PMI: the fee for a small down payment
On a conventional loan with less than 20% down, lenders usually require private mortgage insurance (PMI). It protects the lender, not you. It typically costs about 0.3%–1.5% of the loan amount per year, depending on your credit score and down payment.
On our $320,000 loan, 0.6% PMI comes to $1,920 a year, or $160 a month. That brings the total to roughly $2,785.
When PMI goes away
Under the federal Homeowners Protection Act:
- You can request cancellation once your balance reaches 80% of the home's original value, as long as you're current on payments.
- PMI ends automatically at 78%.
FHA loans work differently. Their mortgage insurance premium (MIP) often lasts for the life of the loan if you put down less than 10%, and the usual way to get rid of it is to refinance.
Tip: the amortization schedule tells you when you'll reach 80% without extra payments. If home values in your area have gone up, some lenders will cancel PMI earlier based on a new appraisal. Ask your servicer.
How extra payments change the schedule
Because interest is charged on the remaining balance, every extra dollar of principal saves interest for the rest of the loan.
With the same $320,000 loan at 6.75%:
| Strategy | Payoff time | Interest saved (approx.) |
|---|---|---|
| Standard payments | 30 years | — |
| +$200/month | ~24.5 years | ~$95,000 |
| One extra payment per year | ~24 years | ~$100,000 |
| 15-year term instead (higher payment) | 15 years | ~$250,000+ |
Mark extra payments as "principal only" so the servicer doesn't just apply them to next month's payment.
Comparing rates and payments in percentages
When you're comparing quotes or deciding whether to refinance, it helps to think in percent change. Going from 7.25% to 6.5% sounds like 0.75 points, but it's a 10.3% decrease in the rate. On a $320k loan that lowers the payment by about $160 a month. A percentage increase/decrease calculator is handy for checking things like how much your escrow went up this year or how much a refinance actually saves.
Key takeaways
- Early payments are mostly interest. That's normal, and it's why paying a little extra early on saves so much.
- PITI = principal + interest + taxes + insurance. Only the first two follow the amortization schedule.
- PMI applies to conventional loans with less than 20% down. You can request cancellation at 80% loan-to-value, and it ends automatically at 78%.
- Extra principal payments, especially in the first 5–10 years, can cut years off the loan and save tens of thousands in interest.
Before you sign, run your actual loan amount, rate and term through an amortization schedule. Seeing month 1 next to month 240 is one of the clearest ways to understand what a mortgage really costs.
This article is for education only and isn't financial advice. Rates, PMI pricing and escrow costs vary by lender and location.
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