You just signed a 30-year mortgage for $300,000 at 7% interest. Your monthly payment is $1,996. Over 30 years, you’ll pay a total of $718,527 — more than double the original loan amount. Wait, what?
It sounds shocking, but that’s exactly how amortization works. Understanding it is the key to making smarter borrowing decisions.
What Is Amortization?
Amortization is the process of paying off a loan through regular, equal payments over a set period. Each payment is split between two things: interest (what the bank charges you for borrowing) and principal (reducing what you actually owe).
The twist is that the split changes over time. Early payments are mostly interest. Later payments are mostly principal.
Why Early Payments Are Mostly Interest
Interest is calculated on your remaining balance. When you start a loan, your balance is at its maximum — so the interest charge is at its maximum too.
Example — Month 1 of a $300,000 loan at 7%:
- Monthly interest rate: 7% ÷ 12 = 0.583%
- Interest charge: $300,000 × 0.00583 = $1,750
- Your payment: $1,996
- Amount going to principal: $1,996 - $1,750 = $246
In the first month, 87.7% of your payment goes to interest. Only 12.3% reduces your debt.
Fast forward to Month 300 (year 25):
- Remaining balance: about $107,000
- Interest charge: $107,000 × 0.00583 = $624
- Amount going to principal: $1,996 - $624 = $1,372
Now 68.7% goes to principal. The balance shrinks faster and faster as you progress.
The Total Cost of Borrowing
The interest rate determines how much extra you pay over the life of the loan.
For a $300,000 mortgage:
| Term | Rate | Monthly Payment | Total Interest Paid |
|---|---|---|---|
| 30 years | 6% | $1,799 | $347,515 |
| 30 years | 7% | $1,996 | $418,527 |
| 30 years | 8% | $2,201 | $492,476 |
| 15 years | 6% | $2,532 | $155,683 |
| 15 years | 7% | $2,696 | $185,367 |
A single percentage point difference on a 30-year mortgage costs roughly $70,000 in extra interest.
How Extra Payments Save You Thousands
Making extra payments — even small ones — directly reduces your principal, which means less interest accrues in every future month. The effect snowballs.
$300,000 mortgage at 7%, 30 years:
- Normal payoff: 30 years, $418,527 in interest
- Extra $100/month: Paid off in 25.5 years, saves $56,000 in interest
- Extra $200/month: Paid off in 22.5 years, saves $98,000 in interest
- Extra $500/month: Paid off in 17.5 years, saves $175,000 in interest
Even rounding up your payment to the nearest hundred can shave years off your loan.
Amortization Applies to All Loans
The same principle works for car loans, student loans, and personal loans — any loan with fixed payments.
Auto loan example: A $35,000 car loan at 6.5% for 5 years has a monthly payment of $685. Total interest paid: $6,100. If you extend to 7 years, the payment drops to $520 but total interest rises to $8,700.
Student loans: Federal student loans typically have 10-year repayment terms. Extending to 25 years lowers payments but dramatically increases total interest.
Calculate Your Loan Payments
Use our free loan calculator to see your monthly payment, total interest, and a full amortization schedule. Try different loan amounts, rates, and terms to find the best option.
For home buyers, pair it with our compound interest calculator to compare what investing the same money could earn.
This article is for informational purposes only and does not constitute financial advice. Please consult a qualified financial advisor for decisions about loans and mortgages.