Mortgage Recast Calculator
Reviewed May 26, 2026
Estimate your new mortgage payment after a lump-sum principal payment. Compare the lower required payment with the faster-payoff path of keeping your old payment.
New balance over remaining term
Same interest rate, same scheduled payoff window, lower required P&I payment.
Need payment relief, not a new loan
Useful when your existing rate is worth keeping and your servicer allows re-amortization.
Lower payment vs. faster payoff
Extra principal without recasting usually saves more interest but keeps the payment higher.
Mortgage Recast Calculator
Estimate how a lump-sum principal payment could lower your required principal-and-interest payment without changing your rate or remaining term.
Current Mortgage
Recast Request
How Mortgage Recasting Works
A mortgage recast starts with a principal curtailment: you make a lump-sum payment that reduces the unpaid balance. The servicer then re-amortizes the lower balance over the remaining scheduled term at the existing note rate. The result is a lower required principal-and-interest payment without a new mortgage, new rate lock, or full refinance closing.
The calculator above uses fixed-rate amortization math. It treats the lump sum as principal only, calculates the new balance, and estimates a new monthly P&I payment. It also shows what happens if you apply the same lump sum but keep paying the old amount: that path usually pays the loan off earlier and saves more interest, but it does not lower the required payment.
Recast Decision Checklist
- Confirm your loan type and servicer allow recasting before wiring or mailing a large principal payment.
- Ask whether the recast fee, minimum lump sum, seasoning period, and payment status rules apply to your loan.
- Compare recast payment relief with simply keeping the higher payment after the lump sum for faster payoff.
- Use the refinance calculator if a new rate, term, or cash-out structure may improve the total cost.
- Keep taxes, insurance, PMI, HOA, and escrow separate from principal-and-interest recast math.
Recast vs. Refinance vs. Extra Principal
| Option | Payment impact | Rate impact | Best when |
|---|---|---|---|
| Recast | Lowers required P&I payment | Keeps current rate | You have a lump sum and want cash-flow relief |
| Refinance | Can lower or raise payment | Creates a new rate and term | A new loan beats your current loan after costs |
| Extra principal only | Keeps required payment the same | Keeps current rate | You want faster payoff and maximum interest savings |
Source Notes and Caveats
Fannie Mae servicing guidance describes additional principal payments as principal curtailments and says servicers may agree to reduce the P&I payment after a substantial principal curtailment by re-amortizing the current unpaid balance using the current interest rate and remaining loan term. CFPB consumer guidance explains the basic principal-and-interest split in mortgage payments and why principal reductions lower the balance that accrues future interest.
- Fannie Mae: Processing Additional Principal Payments
- Fannie Mae: Processing Mortgage Loan Payments and Payoffs
- CFPB: How paying down a mortgage works
Frequently Asked Questions
What is a mortgage recast?
A recast recalculates your required principal-and-interest payment after a lump-sum principal payment. It generally keeps your existing rate and remaining term.
How is the new payment calculated?
The calculator subtracts the lump sum from your current balance, then applies the standard amortization formula to the new balance over the remaining months at the same rate.
Does recasting save more interest than extra payments?
No. The lump sum saves interest either way, but taking the lower recast payment usually saves less interest than keeping the old payment and paying off faster.
Should I recast or refinance?
Use recasting when you want to keep the existing loan and lower required payment. Use the refinance calculator when a new rate, term, or cash-out structure may beat your current loan after costs.