Mortgage Recast Calculator
See how a lump-sum principal payment could change your required monthly principal-and-interest payment. Enter your remaining balance, remaining term, current rate, and proposed principal payment.
Maintained by Archie Chang · Data and formulas checked September 30, 2026 · Methodology & sources
Current Loan and Proposed Recast
Use the unpaid principal balance and remaining term from your latest statement. Enter only the principal curtailment—not the recast fee—in the lump-sum field.
Worked Monthly Payment Example
With a $300,000 remaining balance, a 6.50% rate, and 25 years left, a $50,000 principal payment leaves a $250,000 balance. This calculator estimates that the monthly principal-and-interest payment changes from $2,025.62 to $1,688.02—a difference of $337.60 per month.
If the borrower keeps paying $2,025.62 after the same lump sum instead of recasting, the loan is paid off in 17 years 1 month, 7 years 11 months sooner, with $164,041 of remaining interest instead of $256,405 after a recast.
The example keeps the rate and remaining term the same. It excludes taxes, insurance, and other escrowed charges, so the total amount shown on a monthly statement can differ.
What the Estimate Includes
This tool models the voluntary mortgage re-amortization described by Fannie Mae after a substantial principal curtailment: the new unpaid balance is amortized at the existing rate over the existing remaining term. It compares the scheduled principal and interest before and after that change.
It does not model escrow, mortgage insurance, a changed interest rate, a changed maturity date, taxes, investment returns, or loan-specific qualification rules. A servicer's quote controls the actual contractual payment.
Estimated New Payment
$1,688.02
Monthly principal and interest
- Current P&I payment
- $2,025.62
- Monthly savings
- $337.60
- New principal balance
- $250,000
- Remaining interest saved
- $51,281
- Net savings after fee
- $51,031
- Fee-only cash-flow break-even
- 1 month
Recast or Keep Your Old Payment?
The same lump sum can lower your required payment through a recast, or shorten the loan if you keep paying the old amount. Principal and interest only; the recast fee is not included.
| Scenario | Monthly P&I | Time to payoff | Remaining interest |
|---|---|---|---|
| No lump sum | $2,025.62 | 25 years | $307,686 |
| Lump sum, then recast | $1,688.02 | 25 years | $256,405 |
| Lump sum, keep old payment | $2,025.62 | 17 years 1 month | $164,041 |
Amortization Schedule Before and After the Recast
Loan balance at the end of each year under each scenario, and the interest paid each year after a recast.
| Year | No lump sum | After recast | Keep old payment | Interest paid (recast) |
|---|---|---|---|---|
| 1 | $295,047 | $245,872 | $241,698 | $16,128 |
| 2 | $289,762 | $241,468 | $232,840 | $15,852 |
| 3 | $284,123 | $236,769 | $223,389 | $15,557 |
| 4 | $278,106 | $231,755 | $213,305 | $15,242 |
| 5 | $271,687 | $226,405 | $202,546 | $14,907 |
| 6 | $264,837 | $220,697 | $191,066 | $14,548 |
| 7 | $257,529 | $214,607 | $178,817 | $14,166 |
| 8 | $249,731 | $208,109 | $165,748 | $13,758 |
| 9 | $241,411 | $201,176 | $151,803 | $13,323 |
| 10 | $232,534 | $193,778 | $136,925 | $12,859 |
| 11 | $223,063 | $185,885 | $121,050 | $12,363 |
| 12 | $212,957 | $177,463 | $104,113 | $11,835 |
| 13 | $202,174 | $168,478 | $86,040 | $11,271 |
| 14 | $190,669 | $158,890 | $66,758 | $10,669 |
| 15 | $178,394 | $148,661 | $46,184 | $10,027 |
| 16 | $165,296 | $137,746 | $24,232 | $9,342 |
| 17 | $151,322 | $126,100 | $810 | $8,611 |
| 18 | $136,411 | $113,675 | $0 | $7,831 |
| 19 | $120,502 | $100,417 | $0 | $6,999 |
| 20 | $103,528 | $86,271 | $0 | $6,111 |
| 21 | $85,416 | $71,178 | $0 | $5,163 |
| 22 | $66,092 | $55,075 | $0 | $4,152 |
| 23 | $45,473 | $37,892 | $0 | $3,074 |
| 24 | $23,474 | $19,559 | $0 | $1,923 |
| 25 | $1 | $0 | $0 | $695 |
Mortgage Recast vs. Extra Principal vs. Refinance
| Option | Required payment | Rate and term | Typical tradeoff |
|---|---|---|---|
| Recast | Recalculated lower after approval | Existing rate and remaining term | Uses a lump sum; may require a fee and eligibility review |
| Extra principal only | Usually unchanged | Existing rate; earlier payoff if payments continue | Saves interest but does not normally lower the amount due |
| Refinance | Set by a new loan | May change both | New underwriting and potentially substantial closing costs |
Mortgage Recast Questions
What is a mortgage recast?
A mortgage recast, also called re-amortization after a principal curtailment, recalculates the required monthly principal-and-interest payment after you make a substantial lump-sum principal payment. The remaining balance is spread over the remaining term at the existing interest rate. Your servicer must approve and process it.
How is a recast mortgage payment calculated?
The new payment uses the standard fixed-payment amortization formula with three inputs: the balance after the lump-sum payment, the existing interest rate, and the number of monthly payments remaining. This calculator does not extend the term or substitute a new interest rate.
Does a mortgage recast change the interest rate or loan term?
Normally, no. A recast lowers the unpaid principal balance and recalculates principal and interest over the remaining term using the current note rate. It is different from refinancing, which replaces the loan and may change the rate, term, and closing costs.
Can every mortgage be recast?
No. Eligibility, minimum principal curtailment, fees, seasoning requirements, and processing rules depend on the loan, investor, and servicer. Ask your mortgage servicer for written eligibility and a formal payment quote before sending a lump sum.
Does the new payment include property tax and insurance?
A recast changes only principal and interest. Escrowed property taxes, homeowners insurance and mortgage insurance stay the same and can change on their own schedule. Enter your monthly escrow amount in the calculator to see the total monthly payment before and after the recast.
Should I recast or keep paying the same amount?
After a lump-sum principal payment you can either recast, which lowers the required payment over the same remaining term, or keep paying the old amount, which pays the loan off years earlier and saves more interest. Keeping the payment needs no servicer approval or fee, while a recast lowers the amount you are required to pay each month. The comparison table shows both for your numbers.
Is a mortgage recast the same as making an extra principal payment?
No. An extra principal payment reduces balance and interest, but the required monthly payment normally stays the same unless the servicer completes a recast. Keeping the old payment after a principal reduction can pay the loan off earlier; recasting instead lowers the required payment over the original remaining term.
When can a mortgage recast be worth considering?
A recast may be useful when you want a lower required payment without replacing a favorable mortgage rate. Compare the payment reduction, interest savings, servicer fee, cash you would give up, and alternative uses for that cash. The calculator is an estimate, not a servicer quote or recommendation.
Related calculators
Authoritative sources: Fannie Mae recast loan overview · Fannie Mae additional principal payment guide · CFPB mortgage resources