Financing · Formula v1.0.0
Mortgage Amortization Calculator
See the complete repayment schedule, principal vs interest every month, remaining balance, and how extra payments shorten the loan.
Monthly payment
$1,970.30
Paid off in 30 years
- Loan principal
- $320,000
- Scheduled monthly payment
- $1,970.30
- Number of payments (no extras)
- 360
- Total interest (no extras)
- $389,303
- Total payments (no extras)
- $709,303
- Remaining balance after year 1
- $316,250
- Principal share of first paymentThe rest of the payment is interest
- $303.63
- Principal share of final paymentAmortization flips over time
- $1,955.17
Amortization is the process of repaying a loan in fixed installments where the interest portion shrinks and the principal portion grows over time.
Each month, interest is charged on the remaining balance; whatever part of the payment is left reduces the principal. Because the balance falls, next month's interest is slightly smaller, so slightly more of the same payment retires principal. That feedback loop is the amortization curve.
Adding even small extra amounts to principal can cut years off the schedule, because those dollars avoid interest for the rest of the term.
Interest(t) = Balance(t−1) × r · Principal(t) = Payment − Interest(t) · Balance(t) = Balance(t−1) − Principal(t)
r: Monthly interest rate (annual ÷ 12).
Balance(t): Remaining principal after payment t.
A $320,000 loan at 6.25% for 30 years has a $1,970.30 scheduled payment. Month 1: interest = 320,000 × 0.0052083 ≈ $1,666.67, principal ≈ $303.63.
Without extras the loan runs the full 360 payments and interest totals roughly $389,306.
Adding $200/month of extra principal pays the loan off in 282 months, about 6.5 years earlier, and saves roughly $99,000 of interest (exact figures appear in the results).
- •Monthly frequency only in this release; no biweekly acceleration modeling.
- •No escrow, fees, ARM resets, or prepayment penalties.
Formula reference
Interest(t) = Balance(t−1) × r · Principal(t) = Payment − Interest(t) · Balance(t) = Balance(t−1) − Principal(t)
- r, Monthly interest rate (annual ÷ 12).
- Balance(t), Remaining principal after payment t.