finance calculator
Model an amortization schedule with both recurring extra monthly payments and a one-time lump-sum prepayment. See payoff months, total interest, and savings.
This amortization with prepayments calculator lets you see how both recurring extra monthly payments and a one-time lump-sum prepayment affect your loan’s payoff timeline and total interest.
By combining a small extra amount every month with a larger lump sum when you receive a bonus, tax refund, or other windfall, you can significantly shorten your loan term and reduce interest paid. The calculator simulates the loan month by month and compares the prepayment scenario to a baseline schedule with no extra payments.
Use it to test different payoff strategies for mortgages, auto loans, or other fixed-rate loans before you commit to a plan.
We calculate the standard fully amortizing monthly principal-and-interest payment based on the loan amount, annual interest rate, and term in years.
Using that base payment, we simulate the loan on a monthly basis: each month, interest accrues on the remaining balance and the scheduled payment reduces principal.
If you enter a recurring extra monthly payment, we add that extra amount to every scheduled payment and apply the additional portion directly to principal.
If you enter a lump-sum prepayment and month, we apply that lump sum toward principal in the specified month, in addition to the regular payment and any recurring extras.
We continue the simulation until the loan balance reaches zero, at which point we record the payoff month, payoff years, total interest paid, and total amount paid under the prepayment plan.
Separately, we compute total interest and payoff timing for the baseline schedule with no prepayments, so we can show interest saved and time saved by following your prepayment strategy.
Standard fixed-rate payment:
Let L = loan amount
Let r = monthly interest rate (APR ÷ 12)
Let n = total number of months (years × 12)
Base payment = L × [ r × (1 + r)^n ] ÷ [ (1 + r)^n − 1 ]
Simulation with prepayments:
For each month i until payoff:
Interest_i = Balance_{i-1} × r
Principal_base_i = Base payment − Interest_i
Principal_extra_i = Recurring extra (if any)
Principal_lump_i = Lump sum (only in the chosen lump month)
Total principal_i = Principal_base_i + Principal_extra_i + Principal_lump_i
New balance = max(0, Balance_{i-1} − Total principal_i)
Total interest with prepayments = Σ Interest_i
Interest saved = Total interest without prepayments − Total interest with prepaymentsModel a loan amortization schedule with both recurring extra payments and a one-time lump-sum prepayment to see how much sooner you can pay off your loan and how much interest you might save.
Enter loan details, a recurring extra amount, and a lump-sum prepayment month and amount to compare your prepayment plan against the baseline schedule instantly.
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Loan Amortization Schedule (with Extra Payment)
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This amortization with prepayments calculator is for educational purposes only and provides simplified estimates of payments, payoff timing, and interest savings based on your inputs and a fixed-rate amortization model. It is not a loan offer, payoff quote, or financial advice. Actual loan terms, interest charges, and prepayment handling depend on your lender's policies and your loan agreement. Always review official loan documents and consult qualified professionals before making borrowing, refinancing, or prepayment decisions.