Mortgage Prepayment Calculator
Use the Mortgage Prepayment Calculator
Blend recurring extra payments and one-off lump sums to test mortgage acceleration strategies.
- Lump-sum impact modeling
- Interest reduction analysis
- Mortgage acceleration strategy
Enter the current mortgage terms, recurring extra payment, and each planned lump sum with its expected timing; retain adequate liquidity and verify how the lender applies prepayments.
What this calculator covers
Inputs you can model
- Original principal
- Annual interest rate %
- Term years
- Monthly payment
- Extra monthly payment
- Lump-sum payment
- Lump-sum month
- First repayment date
Results you can review
- Scheduled payment
- Original months
- Accelerated months
- Interest saved
- Months saved
- Original interest
- Accelerated interest
- Original amortization schedule
- Accelerated amortization schedule
Method, policy basis, and limitations
How the estimate is built
The model amortizes the outstanding balance using the entered rate and payment, then applies recurring and scheduled lump-sum principal reductions to compare payoff outcomes.
Important limitation
This is a planning schedule, not a lender payoff statement. Prepayment penalties, recasting rules, escrow, fees, variable rates, and the lender's payment-allocation method may alter savings.
Your inputs
Enter the values you know. Required fields should be completed first, and optional fields can be left blank if they do not apply to your situation.
Run the calculator to see the planning signal, key measures, reconciliation detail, and any schedules or stress scenarios returned for these inputs.
Your results
The top cards show the most important answers first. Detailed schedules, scenario tables, and supporting notes appear underneath for deeper review.
Inputs changed. Run the calculator again to refresh these results; copy, print, PDF, and Excel actions are unavailable until then.
This is a planning schedule, not a lender payoff statement. Prepayment penalties, recasting rules, escrow, fees, variable rates, and the lender's payment-allocation method may alter savings.