Mortgage Recast Calculator
Compare the scheduled payment with a payment recalculated from the post-lump-sum balance and remaining term. A recast changes payment amortization but normally keeps the existing interest rate and maturity date.
How to use the Mortgage Recast Calculator
Enter current principal, annual interest rate, remaining payments, proposed lump sum, and any recast fee.
Review servicer eligibility, minimum lump sum, escrow, fees, exact effective date, and whether the loan is fixed-rate.
Read principal after curtailment, old and recast payments, monthly reduction, and estimated interest savings after the fee.
Formula
New balance = current principal − lump sum. With monthly rate i and n remaining payments, recast payment = new balance × i × (1 + i)^n ÷ ((1 + i)^n − 1).
Example
A $250,000 balance reduced by a $25,000 lump sum is recast from $225,000 using the unchanged rate and remaining number of payments.
Assumptions and limitations
- The model covers principal and interest only, assumes the rate and maturity do not change, and does not represent servicer approval.
- Mortgage Recast Calculator treats the entered values as estimates and does not infer missing project, account, or personal details.
- Calculations retain working precision except where the cited method requires an intermediate rounding step; displayed values are then formatted separately. Source rules and dated rates must be rechecked when they change.
Sources
- Consumer Financial Protection Bureau: Your mortgage servicerMortgage servicing, balances, and payment administration context. Reviewed 2026-08-14.
- U.S. Securities and Exchange Commission: Compound Interest CalculatorCompound-growth inputs and future-value concepts. Reviewed 2026-08-14.
- Fannie Mae: Processing Additional Principal PaymentsOfficial formula, rate, or program guidance used by this calculator. Reviewed 2026-08-14.
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Frequently asked questions
How does the Mortgage Recast Calculator work?
New balance = current principal − lump sum. With monthly rate i and n remaining payments, recast payment = new balance × i × (1 + i)^n ÷ ((1 + i)^n − 1).
What information should I enter in the Mortgage Recast Calculator?
Enter current principal, annual interest rate, remaining payments, proposed lump sum, and any recast fee, then verify servicer eligibility, minimum lump sum, escrow, fees, exact effective date, and whether the loan is fixed-rate.
What should I verify before using this Mortgage Recast Calculator result?
The model covers principal and interest only, assumes the rate and maturity do not change, and does not represent servicer approval.
Reviewed 2026-08-14 · reamortization-v1 · content-2026-08-14 · Trusty Calculator Editorial Team