How loan amortization works
Each payment covers that month’s interest first; the rest reduces principal. That is why early payments barely dent the balance.
Sourced from official pages · Updated September 30, 2026💡 Key takeaways
- With a fixed-rate loan your payment stays the same, but the split between interest and principal changes every month.
- Early payments are mostly interest because the balance is highest.
- Extra principal payments reduce future interest and shorten the loan.
- The payment formula is P × r × (1 + r)^n ÷ [(1 + r)^n − 1].
The basic idea
With a fixed-rate installment loan such as a mortgage or auto loan, your payment is the same every month. Each month the lender charges interest on the current balance; whatever is left of your payment reduces the principal.
Why early payments are mostly interest
At the start, the balance is at its highest, so the monthly interest is highest and the principal portion is small. As the balance falls, the interest portion shrinks and the principal portion grows. On a 30-year loan the balance falls slowly in the first years.
The formula
Payment = P × r × (1 + r)n ÷ [(1 + r)n − 1], where P is the loan amount, r is the monthly rate (APR ÷ 12) and n is the number of monthly payments.
How extra payments help
An extra payment toward principal reduces the balance that future interest is charged on, so it saves more the earlier you make it. Confirm the extra amount is applied to principal and that there is no prepayment penalty. Try it in the mortgage calculator’s extra-payments tool.
Reading an amortization schedule
A schedule lists each payment, how much went to interest, how much to principal and the remaining balance. The mortgage calculator on this site shows the schedule and lets you download it.
Making extra payments work
- Confirm the lender applies extra money to principal.
- Check for a prepayment penalty.
- Pay extra early in the loan for the biggest effect.
- Use a one-time or recurring amount in the extra-payments tool.
🔤 Key terms
| Term | Meaning |
|---|---|
| Principal | The amount you owe, excluding interest |
| Interest | The cost of borrowing |
| Amortization schedule | A table showing each payment’s split |
| Term | Length of the loan |
🧮 Worked example: first payment on a $320,000, 30-year loan at 7.03%
The monthly payment is about $2,135.42. In month 1, interest is about $1,874.67 (the balance × 7.03% ÷ 12), so only about $260.75 goes to principal. Over time the interest share shrinks and the principal share grows. Illustration only.
⚠️ Common mistakes to avoid
- Assuming half of each payment goes to principal from the start.
- Sending extra money without telling the lender it is for principal.
- Ignoring prepayment penalties.
- Comparing loans without looking at total interest.
🛠️ Try it yourself
❓ Frequently asked questions
What is amortization?
The process of paying off a loan through scheduled payments that cover interest and principal.
Does an extra payment shorten the loan?
Yes, if applied to principal.
Do all loans amortize?
Many installment loans do; some loans have balloon payments.
Is an ARM amortized?
Yes; the payment changes when the rate adjusts.
📚 Sources
This guide is general information, not financial, tax or legal advice. Rules and limits change; confirm with the sources above or a licensed professional.