Amortization is the process of paying off a loan through a series of equal monthly payments over a set period. Each payment covers both interest and principal — but the ratio between them shifts dramatically over the life of the loan.
How the Split Changes Over Time
Because interest is calculated on the remaining balance, early payments are dominated by interest. As the balance falls, more of each payment goes to principal. The payment amount stays constant, but the composition changes with every single payment.
On a $350,000 loan at 6.5% for 30 years (~$2,213/mo P&I):
| Year | Principal paid | Interest paid | Balance remaining |
|---|---|---|---|
| 1 | $4,100 | $22,450 | $345,900 |
| 5 | $5,600 | $20,950 | $318,100 |
| 10 | $7,700 | $18,850 | $279,300 |
| 20 | $14,600 | $11,950 | $164,800 |
| 30 | $26,300 | $250 | $0 |
The Power of Extra Payments Early
Because early payments barely touch principal, any extra money you pay in the first few years directly reduces the balance that future interest is calculated on. The compounding effect is significant.
Adding $200/month to the loan above would cut about 5 years and $40,000+ in interest off the loan. The earlier you start, the bigger the impact.
Reading an Amortization Schedule
An amortization schedule lists every payment:
- Payment number and date
- Total payment amount
- Interest portion
- Principal portion
- Remaining balance after that payment
Lenders are required to provide a full amortization schedule when you close on a mortgage. You can also generate one instantly in our calculator.
Shorter Terms = Less Interest, Higher Payments
A 15-year amortization compresses the same payoff into half the time. Your monthly payment is higher, but the total interest is dramatically lower — sometimes less than half of what a 30-year loan would cost.
The trade-off is cash flow. A higher required payment leaves less flexibility. Some borrowers take a 30-year loan and simply make extra payments when they can — capturing most of the interest savings while keeping the lower required payment as a safety net.
Negative Amortization: When Balances Grow
Some loan products (common before 2008) allowed minimum payments that didn't even cover monthly interest. The unpaid interest was added to the principal — meaning the balance grew over time. This is called negative amortization. Standard conventional, FHA, and VA loans today are fully amortizing and do not have this risk.