The schedule is a repeated calculation
An amortization schedule traces a loan through time. For each month, calculate interest on the opening balance, subtract that interest from the payment to find principal repaid, and deduct the principal from the balance. The next month starts from the result. A fully amortizing loan reaches zero by its scheduled last installment.
Why the balance curve is not a straight line
With an unchanged rate and fixed payment, interest consumes a larger share when the balance is larger. As debt falls, the same payment can repay more principal. The shape comes from that arithmetic, not from a lender withholding principal credit during the first years.
A zero-interest example makes the contrast clear. A $120,000 loan repaid over 120 equal months has a $1,000 monthly payment and a straight-line balance decline. At a positive rate, some of each payment funds interest, so the principal trajectory changes. The calculator handles the zero-rate case separately to avoid dividing by zero.
Loans that do not follow the standard pattern
Interest-only periods, balloon maturities and negative amortization can interrupt the ordinary path to zero. With negative amortization, unpaid interest can be added to the balance when the payment is insufficient to cover it. A balloon loan can have regular payments yet still require a substantial balance at maturity.
Build a schedule that matches the question
For an original schedule, enter the original amount and full term. For a forward-looking estimate from today, enter the current principal and remaining term. Those two schedules have different starting points. If the loan has already had extra payments, the original schedule may no longer match its balance.
The remaining-balance tool selects a row from an original schedule. The extra-payment tool models new principal contributions. The interest-only and balloon tools expose those structures explicitly. Choosing the appropriate model is more useful than adding precision to inputs that describe the wrong loan.
Rounding and real servicing
The engine retains unrounded numbers internally and rounds the display to cents. Servicers may use different contractual conventions, posting dates or daily-interest calculations. Small differences can therefore appear even with accurate inputs. Large differences deserve a check of the balance, remaining term, rate and payment history.
The table’s total interest excludes property tax, insurance and association charges. Those are real household expenses, but including them under an “interest” label would make the schedule harder to interpret. Use the mortgage payment calculator for the broader monthly budget.
Questions, answered
Can I download the schedule?
Yes. Calculator pages with a schedule provide a CSV download of the current result.
Why is the last payment sometimes smaller?
The final installment is capped at the debt and interest still due in the model.
Sources
- Mortgage key terms. Consumer Financial Protection Bureau. Accessed 2026-09-09.
- What is negative amortization?. Consumer Financial Protection Bureau. 2024-09-13. Accessed 2026-09-09.