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Mortgage Recast Calculator

This calculator estimates how a lump-sum principal payment plus a loan recast changes your mortgage balance, monthly payment, and interest over the remaining term. Enter your current balance, rate, remaining term, payment, recast amount, lender fee, and preferred new term to compare the post-recast payment schedule.

Assumptions used by this calculator

  • Interest model: Fixed rate applied to the remaining balance after the lump-sum principal reduction
  • Recast fee: Entered separately; does not reduce principal unless your lender applies it that way
  • Prepayment / escrow: Taxes, insurance, and HOA are not included in payment math

Quick start: Fill in your current loan details, the lump sum you will apply, any recast fee, and the new term your lender will use.

Last updated:

Remaining Term
New Term

Mortgage Recast Results

Recast Mortgage Balance: $
Monthly Payment: $
Total # Of Payments:
Total Interest Paid: $
Total Payment: $

How to use the Mortgage Recast Calculator

  1. Current loan amount: Enter the remaining principal before the lump sum.
  2. Interest rate: Use your note rate (APR differences from fees are not modeled).
  3. Remaining term: Years and optional months left on the loan.
  4. Current monthly payment: Principal and interest payment you make today.
  5. Recast amount: Lump sum applied to principal.
  6. Recasting cost: Lender/servicer fee for the recast.
  7. New term: Term used after the recast (as agreed with your lender).
  8. Click Calculate Savings to see the new balance and payment figures.

How the calculation works

The tool subtracts the recast lump sum from the current balance to get a new principal, then amortizes that balance over the new term at your stated interest rate to estimate the revised monthly principal-and-interest payment and lifetime interest on that schedule.

Formula / methodology

After the lump sum, principal is:

New Balance = Current Balance − Recast Amount
  • The new payment is the standard fixed-rate amortization payment for New Balance, rate, and new term.
  • Interest totals assume on-time payments and no extra principal beyond the modeled schedule.

Example calculation

Example: $300,000 balance at 4.5% with 30 years remaining, a $1,500 current P&I payment, a $50,000 recast principal payment, a $250 fee, and a 25-year post-recast term.

The calculator reduces the balance to about $250,000, then re-amortizes that amount over 25 years at 4.5% to show the new monthly payment and interest totals in the results table.

Understanding your result

Focus on the new monthly payment and total interest after the recast. Compare those to keeping your current payment (which would pay the loan off faster after a lump sum without a recast). A lower payment improves cash flow; keeping the old payment after a principal reduction usually saves more interest.

Limitations / assumptions

  • Does not include taxes, insurance, PMI, or escrow changes.
  • Does not model variable rates, negative amortization, or interest-only periods.
  • Lender rules for minimum recast amounts and fees vary; the fee field is an estimate you provide.
  • Not a lender quote or legal/financial advice.

Frequently asked questions

What is a mortgage recast?

A recast applies a lump sum to principal and then recalculates the monthly payment over a remaining (or new) term at the same interest rate, usually without refinancing into a new loan.

Is a recast the same as a refinance?

No. A refinance replaces the loan (often changing the rate). A recast keeps the existing rate and re-amortizes after a principal reduction.

Do all lenders allow recasts?

No. Confirm eligibility, minimum lump sum, fees, and whether the term can change with your servicer before relying on these results.

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