See how each loan payment splits between principal and interest over the full term.
Early in a loan's life, more of each payment goes to interest; later payments shift toward principal.
Amortization is the process of paying off a loan through a series of fixed, regular payments, each of which is split between interest and principal. Early in the loan's life, most of each payment goes toward interest because the outstanding balance is still high. As the balance shrinks, a growing share of each payment goes toward principal — even though the total payment amount stays the same for a fixed-rate loan.
Where P is the loan principal, r is the periodic interest rate (annual rate ÷ number of payments per year), and n is the total number of payments. On a $200,000 loan at 6% over 30 years (360 monthly payments), the fixed monthly payment works out to roughly $1,199 — but in month 1, about $1,000 of that is interest, while by month 300 the split has almost fully reversed.
| Year | Interest paid so far | Principal paid so far | Remaining balance |
|---|---|---|---|
| 5 | $57,700 | $14,300 | $185,700 |
| 10 | $107,900 | $36,100 | $163,900 |
| 20 | $179,300 | $107,300 | $92,700 |
| 30 | $231,700 | $200,000 | $0 |
Remaining balance vs. cumulative interest/principal — $200,000 loan, 6%, 30 years
Example 1 — Standard 30-year mortgage: A $300,000 loan at 6.5% over 30 years has a monthly payment of about $1,896. In month 1, roughly $1,625 goes to interest and only $271 to principal. By year 15, the split is roughly even; by year 29, almost the entire payment goes to principal.
Example 2 — Shorter 15-year term: The same $300,000 at 6.5% but over 15 years raises the payment to about $2,614, yet total interest paid drops from roughly $382,000 (30-year) to about $170,700 — less than half — because the balance is paid down far faster.
Example 3 — One extra payment per year: Adding a single extra full payment each year to a 30-year, $250,000 loan at 6% can shorten the payoff by roughly 4–5 years and save tens of thousands of dollars in interest, without refinancing.
| Amortizing loan | Interest-only / simple interest | |
|---|---|---|
| Payment structure | Fixed payment, split between principal & interest | Interest paid separately; principal often due later |
| Balance over time | Gradually declines to zero | Stays flat until a lump-sum payoff |
| Common uses | Mortgages, auto loans, personal loans | Some business loans, bonds, credit lines |
Why does my early interest seem so high compared to principal? Interest is charged on the outstanding balance, which is largest at the start of the loan, so the interest portion of each payment is largest then too.
Does paying extra always help? For most amortizing loans without prepayment penalties, yes — extra payments reduce the principal balance faster, which reduces future interest charges.
Is amortization the same for all loan types? The same mechanics apply to mortgages, auto loans, and personal loans; only the rate, term, and payment frequency differ.
What is negative amortization? It happens when a payment is smaller than the interest due, so unpaid interest gets added to the principal balance instead of reducing it — the loan balance grows rather than shrinks.
Does the amortization schedule change if I refinance partway through? Yes. Refinancing effectively starts a new loan with a new principal (the remaining balance), rate, and term, so the schedule resets from that point.
Why do two loans with the same rate and term have different total interest? Total interest scales with the principal amount, so a larger loan balance produces more total interest even at an identical rate and term.
Is it better to make biweekly or one extra monthly payment? Both accelerate payoff similarly since biweekly payments (26 half-payments a year) equal 13 monthly payments a year — one more than the standard 12 — so the effect is close to making one extra payment annually.
Do amortization schedules apply to adjustable-rate loans? Yes, but the schedule recalculates each time the rate resets, since payment and the interest/principal split depend on the current rate at that point.
On a $200,000 loan at 6% over 30 years, the very first payment of about $1,199 includes roughly $1,000 in interest and only $199 in principal. By year 20 of the same loan, a similar $1,199 payment includes roughly $770 in principal and just $429 in interest — the split has essentially reversed.
Amortization schedule: A table showing each payment's split between principal and interest across the full loan term.
Remaining balance: The amount of principal still owed at any point in the loan term.