Mortgage Prepayment

This tool models the effect of making an extra lump-sum (or recurring monthly) payment on an existing mortgage. Given loan amount, annual interest rate, original term, repayment method (equal-principal-interest or equal-principal), months already paid, and prepayment details, it recomputes the amortization and compares two handling strategies: shortening the remaining term versus reducing the monthly payment.

1. Under Loan Info, enter Loan Amount (10,000-50,000,000), Interest Rate %, Loan Term in years (1-50), and pick the Repayment Method radio (Equal Principal and Interest or Equal Principal). 2. Under Paid Info, enter Paid Months elapsed so far (0-360). 3. Under Prepayment Info, enter Prepayment Amount, choose One-time or Monthly, and for Monthly optionally set Extra Payment Duration. 4. Choose the handling: Shorten Term (single result, recommended) or Reduce Payment (opens comparison view of both strategies). 5. Optionally expand Penalty Settings to pick a preset penalty rule (time-based or custom amount). 6. Click Calculate, then use Save (named record), Export to CSV, or Saved Records to review history.

Shorten Term keeps the monthly payment roughly the same and removes months from the end of the schedule, maximizing interest saved. Reduce Payment keeps the original payoff date but lowers the monthly payment going forward. The comparison view shows side-by-side: new monthly payment, new total payment, new total interest, remaining months, interest saved, and months saved (shorten-term only), plus a recommendation badge. The payment schedule table highlights the prepayment month in yellow and shows saved interest per period.