US Mortgage Recast Calculator
Estimate how an approved lump-sum mortgage recast changes your payment. Compare reamortizing with keeping the original payment after the same principal reduction.
Rule year: 2026 · USD · Sources checked
Monthly payment after approved recast
Fully amortizing fixed-rate principal-and-interest model, monthly interest, fee paid upfront. No escrow, insurance, programme eligibility, lender minimum, rate change or financed recast fee. The no-recast comparison keeps the modeled original payment, not an arbitrary payslip or escrow-inclusive figure.
For informational purposes only. This estimate is not financial advice, a tax return, a payroll calculation or a lender decision. See the supported circumstances and exclusions below.
How this calculator works
A recast recalculates required principal-and-interest payments after principal is reduced, while keeping the stated rate and remaining maturity. Refinancing replaces the loan and can change both. This model compares the lower recast payment with an original-payment alternative: after the same lump sum, keeping the old payment generally shortens repayment instead. Actual servicer permission and minimum lump sums remain contract matters.
Formula and rules
New principal = balance − lump sum. Recast payment = amortizing payment(new principal, same rate, remaining months). Compare lifetime interest and the separate fee.
Assumptions and limitations
Fully amortizing fixed-rate principal-and-interest model, monthly interest, fee paid upfront. No escrow, insurance, programme eligibility, lender minimum, rate change or financed recast fee. The no-recast comparison keeps the modeled original payment, not an arbitrary payslip or escrow-inclusive figure.
Worked example
At 0% with $120,000 and 120 months left, a $20,000 lump sum reduces the required payment from $1,000 to $833.33. Keeping $1,000 instead clears $100,000 in 100 months; a $250 fee is an additional cash cost.
- Monthly payment after approved recast
- $833.33
- Current principal-and-interest payment model
- $1,000.00
- Monthly payment reduction
- $166.67
- Recast interest over remaining term
- $0.00
Official sources and review
Reviewed against the sources below on 2026-10-07. Rates are held in versioned rule modules. Versioned rules, official source review and year-specific calculation tests.
- Fannie Mae: mortgage payments and principal curtailments ↗
Servicer handling of principal curtailment and permitted re-amortization; no borrower eligibility claim.
Common questions
Does a lump sum automatically recast the loan?
No. A servicer must permit and process a recast. A principal payment alone may leave the required payment unchanged.
Is recasting the same as refinancing?
No. This model retains rate and maturity. Refinance compares a replacement loan, new rate, term and closing costs.
Does a recast always save more interest?
Not compared with continuing the larger payment after the same lump sum. The required-payment reduction and interest result answer different questions.