Amortization Schedule Calculator

• Works for any fixed-rate loan — mortgage, auto, personal or student loan — not just home purchases.
• Switch between a yearly summary and the full month-by-month schedule.
• Add a monthly, annual or one-time extra payment to see the new payoff date and interest saved.
• Every number comes from the same amortization formula lenders use, shown in full below.

How to use this calculator

Enter the loan amount, the annual interest rate, and the term in years. That's enough to produce the full schedule. Choose "Yearly summary" for a compact view of how the balance falls over time, or "Full monthly schedule" to see every individual payment — useful for checking a specific month against a lender's own amortization table.

The Advanced section lets you model extra payments three ways: a fixed amount added every month, a lump sum added once a year, and a single one-time extra payment in a month you choose. All three can be combined, and all three are assumed to reach the principal balance immediately rather than being held by the lender as a prepaid installment — confirm that assumption with your own servicer before relying on the numbers.

The formula behind the schedule

A fixed-rate, fully amortizing loan uses one formula to find the level payment that reduces the balance to exactly zero on the final scheduled payment:

M = P × [ i(1 + i)^n ] / [ (1 + i)^n − 1 ]

M = level monthly payment
P = loan amount
i = annual interest rate ÷ 12
n = number of monthly payments (years × 12)

That payment amount never changes on a fixed-rate loan. What changes every month is how it splits between interest and principal:

interest_this_month  = balance × i
principal_this_month = M − interest_this_month + any extra payment
new_balance          = balance − principal_this_month

Because interest is charged only on the balance still outstanding, and that balance is largest at the very start of the loan, the earliest payments are mostly interest. As the balance falls, less of each payment is consumed by interest and more goes to principal — the same payment amount does increasingly more work later in the loan.

A worked example

A $300,000 loan at 6.5% over 30 years produces a scheduled payment of $1,896.20. In the very first month, interest is $300,000 × 0.0054167 = $1,625, and only $271.20 of that first payment reduces the balance. By roughly the halfway point of the term the split is close to even, and by the final few years almost the entire payment is principal.

Over the full term, total interest on this loan comes to roughly $382,633 — more than the loan itself is at 6.5% over 30 years, which is the single clearest illustration of why the rate and the term both matter as much as the loan amount.

How extra payments change the schedule

Every dollar applied as an extra payment reduces the principal balance immediately, which reduces every future month's interest charge for the rest of the loan. There is no separate "extra payment formula" — the calculator simply re-runs the same month-by-month arithmetic with a larger principal reduction in the months you specify, and the loan finishes early once the balance reaches zero.

A useful way to think about it: paying extra on a loan is mathematically identical to earning a guaranteed, risk-free return equal to the loan's interest rate, because that is exactly the interest charge being avoided. Whether that beats another use of the same money — investing it, paying off higher-rate debt first, or building an emergency fund — depends on your own situation, not on the math of the loan itself.

Assumptions and limitations

• The rate is fixed for the whole term. An adjustable-rate loan will have a different real schedule once the rate resets.
• Extra payments reach principal immediately. Some servicers hold extra payments as a prepaid installment instead of applying them to principal right away — instruct your servicer in writing on every payment if this matters to you.
• No fees, taxes, insurance or PMI are included. This is the loan payment alone. For a mortgage specifically, including property tax, insurance and PMI, use the Mortgage Payment calculator.
• Rounding. Real lender schedules sometimes round the final payment slightly to bring the balance to exactly zero; this calculator does the same but small cent-level differences against a specific lender's own schedule are normal.

Common mistakes

Assuming the payment amount tells you the interest rate. Two loans with the same payment can have very different rates and terms. Always check the rate and term separately.

Expecting extra payments to lower the required monthly payment. On a standard fixed loan, extra principal payments shorten the term rather than reduce the scheduled payment — the payment stays the same until the loan is paid off, just sooner.

Confusing this with a mortgage payment estimate. This calculator produces the loan payment only. For a home purchase, property tax, insurance, PMI and HOA dues typically add a substantial amount on top — see the Mortgage Payment calculator for the full picture.

Frequently asked questions