This Amortization Calculator shows the monthly payment, total interest, and how much of each payment goes toward principal versus interest, year by year, over the loan’s full term.
| Year | Interest Paid ($) | Principal Paid ($) | Remaining Balance ($) |
|---|---|---|---|
| 1 | 11,164 | 15,529 | 84,471 |
| 2 | 9,198 | 17,508 | 66,963 |
| 3 | 6,982 | 19,737 | 47,226 |
| 4 | 4,484 | 22,250 | 24,976 |
| 5 | 1,694 | 24,976 | 0 |
Calculate a Loan’s Full Amortization Schedule and What Extra Payments Change
This calculator breaks a loan into its monthly payment, its total interest cost, and a year-by-year schedule of principal and interest. It’s built for anyone comparing loan offers or testing how an extra monthly payment shortens a mortgage, auto loan, or personal loan.
What to Enter and What the Results Show
Enter total loan amount, the annual interest rate (APR), loan term in years, and an optional extra monthly payment. Results show the required monthly payment, total interest over the life of the loan, first-year principal and interest split, and how much time and interest an extra payment saves, plus a year-by-year schedule table.
How the Monthly Payment and Interest Are Calculated
The payment uses the standard amortization formula from financial mathematics:
$$M = P \times \frac{r(1+r)^n}{(1+r)^n – 1}$$
P is the loan amount, r is the monthly interest rate (the annual rate divided by 12), and n is the total number of monthly payments (loan term in years times 12).
Every dollar of an extra monthly payment goes straight to principal in this calculator’s math, since the required payment already covers that month’s interest. A smaller balance means less interest builds up the following month, which is why extra payments save more interest than their raw dollar total suggests, and why the savings grow the earlier they start.
The most common input mistake is entering the interest rate as a decimal, 0.12, instead of a percentage, 12.0. The calculator already divides by 100 internally, so a decimal entry makes the loan look nearly interest-free.
Loan amount has to be greater than zero, and term has to be at least one year. A 0% rate is valid: the formula would divide by zero, so the calculator switches to simple math instead, loan amount divided by the number of payments, with no compounding to model.
Extra payments can’t be negative. If a payment, extra included, would ever overpay the last bit of principal, the calculator trims that final payment down to exactly the remaining balance rather than showing a negative payoff.
Loan terms are capped at 100 years in the schedule table, so anything entered beyond that won’t display a complete payoff, just a schedule that stops at year 100 with balance left over.
These numbers are a projection based on the loan terms you enter, not a loan estimate or a lender’s commitment, and this calculator isn’t tax, legal, or financial advice.
Why “Extra Payment” Here May Not Match What Your Lender Actually Does
This calculator assumes every dollar of your extra monthly payment reduces principal automatically, every month. Real loan servicing doesn’t always work that way. Per CFPB guidance on mortgage servicing, extra money sent with a payment isn’t guaranteed to reduce your balance unless you specifically direct it to principal.
Some servicers apply it toward your next scheduled payment instead, which doesn’t shorten the loan at all. And even when extra payments do reduce principal as intended, your required monthly payment usually doesn’t drop to match; the loan simply finishes earlier, unless you separately ask your servicer to re-amortize the loan around the new, lower balance.
Principal vs. Interest by Year
Every bar is close to the same height, since the payment barely changes year to year. What shifts is the split inside it: interest shrinks from nearly half the first year’s payment to almost nothing by the last year, while principal takes up the rest.
Common Questions About This Amortization Calculator
Why does the same monthly payment cover less interest each year?
Interest is calculated on the remaining balance. As principal drops, less balance is left to charge interest on, so more of each level payment goes toward principal instead, even though the payment amount doesn’t change.
Does my extra payment reduce my required monthly payment?
Not usually. It shortens the loan instead. Your servicer would need to re-amortize the loan around the lower balance for the required payment itself to drop, and that isn’t automatic.
What happens if I enter a 0% interest rate?
The calculator switches to simple division: loan amount divided by the number of months. There’s no compounding to model, so principal drops by the same amount every payment.
Is my extra payment guaranteed to go toward principal?
Not automatically. Per CFPB guidance, some servicers apply extra money to your next scheduled payment instead unless you specifically direct it toward principal.
Can I model a 100-year loan term?
You can enter one, but the schedule table stops at 100 years (1,200 months) to keep the page responsive. Anything longer won’t display a complete payoff.