Loan Amortization Calculator
Enter your loan amount, interest rate, and term to see your monthly payment and a year-by-year amortization schedule.
What Is Loan Amortization?
Amortization — from the Latin amortire, meaning "to kill off" — is the systematic repayment of a debt through a series of fixed, scheduled payments. With a fully amortizing loan, every payment covers both the accrued interest and a slice of the principal, and the loan balance reaches exactly zero on the final payment date. Nothing is left over; nothing is owed.
Most consumer loans work this way: mortgages, auto loans, personal loans, and federal student loans are all amortizing. The structure gives borrowers predictability — the same payment every month, for the full term — while giving lenders a guaranteed return. It also means that the "true cost" of borrowing is not just the interest rate, but the total interest paid over the full loan term, which is determined by both the rate and the length of the loan.
Understanding how amortization works — specifically, how the interest/principal split evolves over time — is one of the most practically useful things a borrower can know. It explains why extra payments early in a loan save so much more than extra payments late in the loan, and why refinancing mid-loan is not always the savings it appears to be.
The Amortization Formula
The monthly payment for a fixed-rate, fully amortizing loan is:
- M = monthly payment
- P = loan principal (amount borrowed)
- r = monthly interest rate (annual rate ÷ 12)
- n = total number of monthly payments (years × 12)
For each individual payment period, the interest charge is simply the current outstanding balance multiplied by the monthly rate. The principal paid is the total payment minus that interest charge. Because the balance falls after each payment, the interest charge falls too — and more of the fixed payment chips away at principal. The amortization schedule is the month-by-month record of this process.
How the Interest/Principal Split Shifts Over Time
The most important thing to understand about amortization is how dramatically front-loaded the interest payments are. In the early life of a long-term loan, the vast majority of each payment is interest. This table shows the split at different points in a $20,000 loan at 7% for 5 years (monthly payment: $396):
| Payment # | Interest | Principal | Remaining Balance |
|---|---|---|---|
| 1 | $117 | $279 | $19,721 |
| 12 | $95 | $301 | $16,007 |
| 30 | $60 | $336 | $9,881 |
| 48 | $18 | $378 | $2,682 |
| 60 (final) | $2 | $394 | $0 |
Loan Term and Total Interest: The Real Cost of Borrowing
The monthly payment is not the same as the cost of a loan. Stretching a loan term to reduce monthly payments significantly increases the total amount paid. This table uses a $20,000 loan at 7% annual interest to show how term length affects total cost:
| Loan Term | Monthly Payment | Total Interest | Total Paid |
|---|---|---|---|
| 3 years | $617 | $2,211 | $22,211 |
| 5 years | $396 | $3,761 | $23,761 |
| 7 years | $299 | $5,143 | $25,143 |
| 10 years | $232 | $7,841 | $27,841 |
The 10-year loan has a monthly payment $385 lower than the 3-year loan — but costs $5,630 more in total. Whether that trade-off makes sense depends entirely on your cash flow needs and what you would do with the $385 difference each month. If you can invest it at a return exceeding 7%, the longer loan may make financial sense. If it will simply be spent, the shorter term is almost certainly better.
The Consumer Financial Protection Bureau maintains resources explaining amortization and offers tools for comparing loan scenarios before you commit to a borrowing decision.
The Power of Extra Principal Payments
Because interest accrues on the remaining balance, any extra payment that reduces the principal has an outsized long-term effect. Each dollar of principal eliminated today removes a dollar from every future interest calculation for the remaining life of the loan.
On a $300,000 mortgage at 6.5% for 30 years (monthly payment: $1,896), adding $300/month in extra principal payments from day one saves approximately $100,000 in total interest and shortens the loan to about 22 years. The math is not linear — the savings compound because eliminating principal early removes it from the calculation for all remaining periods.
A practical approach: when you receive a tax refund, bonus, or any windfall, direct a portion to loan principal. Even a one-time $2,000 lump sum on a 30-year mortgage at 7% saves roughly $5,000–$8,000 in total interest, depending on when in the loan life you make the payment.
Frequently Asked Questions
What is loan amortization?
Loan amortization is the process of paying off a debt through a fixed schedule of equal periodic payments. Each payment covers two things simultaneously: the interest that has accrued since the last payment, and a portion of the remaining principal. Because interest accrues on the outstanding balance, the interest portion of each payment shrinks over time while the principal portion grows — even though the total payment never changes. By the final payment, the balance reaches exactly zero. This structure is used for most consumer loans: mortgages, auto loans, personal loans, and student loans.
How is the monthly payment calculated?
The standard amortization formula is: M = P × [r(1+r)^n] ÷ [(1+r)^n − 1], where P is the loan principal, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of payments (years × 12). The formula ensures that every equal payment covers exactly the accrued interest plus enough principal so the balance reaches zero on the last payment. For a $25,000 loan at 6% for 5 years: r = 0.005, n = 60. Monthly payment = $483.32. Over 60 payments you pay $28,999 total — meaning $3,999 in interest.
Why do I pay mostly interest at the start of a loan?
Interest accrues on the outstanding balance each period. When you first take out a loan, the balance is at its maximum, so the interest charge is at its maximum. Since the payment is fixed, a large chunk goes to interest and only a small amount reduces the balance. As the balance falls, each period's interest charge is smaller, which means more of the same payment goes toward principal. This front-loading of interest is why paying off a loan early in its life saves so much — you are eliminating future interest charges that would have accrued on a still-high balance.
What happens if I make extra principal payments?
Every extra dollar applied to principal reduces the balance immediately and permanently. Because future interest is calculated on the remaining balance, a smaller balance means less interest accrues in every subsequent period. This has a compounding benefit: the savings grow the longer the loan has left to run. On a $300,000 mortgage at 6.5% with 30 years remaining, adding $200/month in principal payments saves approximately $66,000 in total interest and cuts about 4 years off the loan. You should confirm with your lender that extra payments are applied to principal rather than credited as early next-payment.
What is the difference between amortizing and interest-only loans?
An amortizing loan requires payments of both principal and interest from the start, so the balance declines with every payment. An interest-only loan — common in certain mortgages and construction loans — requires only interest payments for an initial period (typically 5–10 years), meaning the principal balance does not decrease at all during that time. After the interest-only period ends, the loan converts to fully amortizing with much higher payments, since the same principal must now be paid off in a compressed timeframe. Interest-only structures lower initial payments but carry significant risk if property values fall or income does not grow as expected.
How does loan term length affect total interest paid?
Loan term has an enormous effect on total interest cost. Longer terms mean lower monthly payments but far more total interest, because you carry a balance for more years. On a $20,000 loan at 7%, a 3-year term costs $2,211 in total interest; a 10-year term costs $7,841 — 3.5 times as much — for the same loan at the same rate. The monthly payment on the 10-year loan is lower ($232 vs. $617), but you end up paying nearly $4,000 more over the life of the loan. When evaluating loan offers, always compare both the monthly payment and the total cost, not just the payment.
Can I pay off a loan early without penalty?
Most consumer loans today — personal loans, auto loans, and mortgages — do not carry prepayment penalties, but some do. Mortgages on older properties or certain specialty loan programs may include prepayment penalty clauses that charge a fee if you pay off the loan within the first 3–5 years. Always read the loan agreement before signing, and ask the lender explicitly about prepayment penalties if early payoff is something you anticipate. The CFPB's mortgage rules restrict prepayment penalties on many types of residential loans, but the rules vary by loan type.