finance calculator

Amortization with Prepayments (Recurring + Lump Sum)

Model an amortization schedule with both recurring extra monthly payments and a one-time lump-sum prepayment. See payoff months, total interest, and savings.

Results

Standard monthly payment (P&I): $1,580
Monthly payment with recurring extra: $1,580
Months to payoff with prepayment: 360.00
Years to payoff with prepayment: 30.00
Total interest with prepayment: $318,861
Total interest without prepayment: $318,861
Interest saved vs no prepayment: $0
Total paid with prepayment: $568,861

How to use this calculator

Enter loan amount, APR, and term.
Enter a recurring extra monthly payment (or leave zero).
Optionally enter a lump-sum amount and the month you’ll apply it.
Review payoff months/years, total interest with/without prepay, and interest saved.

Inputs explained

Recurring extra: Fixed amount added to each monthly payment and applied to principal.
Lump-sum month: Month number when the lump sum is applied (e.g., 1 = first payment, 13 = after first year).

How it works

We calculate the standard amortized payment.

We simulate amortization month-by-month adding the recurring extra to each payment and applying a one-time lump sum at the chosen month.

We compare payoff timing and total interest to the base schedule without prepayments.

When to use it

Modeling a bonus/tax refund lump sum plus rounding up monthly payments.
Comparing strategies: recurring extra only vs lump sum only (set the other to zero).
Sharing a quick amort summary without exporting a full spreadsheet.

Tips & cautions

Test different lump months to see how earlier prepayments boost savings.
If you only want recurring extras, set lump sum to zero. For lump-only, set recurring extra to zero.
This ignores escrow/fees—focus on principal and interest effects.
Fixed-rate only; no PMI/escrow/fees.
Assumes constant recurring extra and a single lump event; not a full editable spreadsheet.

Deep dive

Model loan amortization with both recurring extra payments and a one-time lump-sum prepayment to see payoff months and interest saved.

Enter loan details, extra amount, and lump month to compare against the base schedule instantly.

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