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Mortgage Recast Calculator
A recast keeps your loan but shrinks the payment. Give this mortgage recast calculator your balance, rate and a one-time lump sum and it returns the new monthly payment, the interest you save and whether the recast fee earns its keep.
See how this works on a $300,000 recast — 3 real examples
New monthly payment (principal & interest)
$0
down from $0 — you save $0/mo
Balance after lump sum
$0
Total interest saved
$0
Fee break-even
—
Remaining term
—
Balance over time
Compare your options
| Scenario | Monthly payment | Payoff time | Remaining interest |
|---|---|---|---|
| Do nothing (keep the loan) | $0 | — | $0 |
| Recast (lower payment, same term) | $0 | — | $0 |
| Lump sum, no recast (keep old payment) | $0 | — | $0 |
Both options apply the same lump sum. Recasting lowers your required payment; keeping the old payment shortens the loan and saves the most interest.
Balance year by yearNo change vs. recast vs. lump sum
| Year | No change | Recast | Lump sum, no recast |
|---|
How the mortgage recast formula sets your new payment
A recast subtracts your lump sum from the current balance, then re-amortizes what is left over the same remaining term at the same rate. The new payment comes from the standard mortgage payment formula:
M = (B − L) · i / (1 − (1 + i)−n)
where B is your current balance, L the lump sum, i the monthly rate (annual rate ÷ 12) and n the number of months remaining. Because n is unchanged, the payoff date stays fixed and only the payment falls. Total interest saved is the remaining interest on the original schedule minus the remaining interest on the recast schedule. The lump-sum-only scenario keeps your old payment: the extra (old payment − new payment) each month goes to principal, so the loan pays off early and saves more interest, which is why recasting trades interest savings for a lower monthly bill. The recast fee is not part of the payment — the calculator compares it separately against the interest you save. Payments assume principal and interest only (taxes, insurance and any PMI are excluded).
Three checks against the same loan
One $300,000 loan at 6.5% with 25 years left, re-figured after three different checks — no new loan, no new rate, no moved payoff date.
A $25,000 check against $300,000
per month$1,856.82
- The bill falls from $2,025.62 to $1,856.82 — $168.80 a month back in the budget.
- Interest over the remaining 25 years shrinks by $25,641, a little more than the check itself.
- Nothing else moves: same rate, same payoff date, the same 25 years still on the clock.
For roughly a $250 fee, $25,000 buys a permanently smaller bill on the same schedule.
Load this example (opens in a new tab)Doubling the check to $50,000
per month$1,688.02
- Twice the lump sum, exactly twice the relief — $337.60 a month instead of $168.80.
- Interest savings climb to $51,281, within a dollar of double the smaller recast's $25,641.
- The new bill of $1,688.02 keeps the old 6.5% rate and the old finish line.
The math is straight-line: every extra dollar in the check works as hard as the first.
Load this example (opens in a new tab)A third of the debt, gone at once
per month$1,350.41
- Wiping out a third of what is owed cuts the payment by exactly a third, to $1,350.41.
- That frees $675.21 every month — four times what the $25,000 version delivers.
- Interest saved reaches $102,562, double the $50,000 result, yet the term never shortens.
A six-figure check buys a payment a third smaller — and not a day off the finish line.
Load this example (opens in a new tab)Illustrations only, not financial advice. Your own rate, taxes and insurance will differ — check with a qualified financial advisor before acting on any of this.
Home mortgage recasting in plain English
- A recast re-amortizes, it doesn’t refinance. A lump sum is applied to principal and the remaining balance is spread over your same term at your same rate — only the payment drops.
- Your rate and payoff date don’t move. That makes recasting a pure cash-flow tool: lower monthly bill, identical finish line, no appraisal or closing costs.
- Recast vs. prepay is a real trade-off. Applying the same lump sum and keeping your old payment shortens the loan and saves the most interest; recasting trades some of that interest for a smaller required payment.
- Eligibility is limited. Conventional and most jumbo loans qualify; FHA, VA and USDA loans generally cannot be recast — you’d refinance instead.
- The fee is small and pays for itself fast. Expect a flat ~$150–$500 charge and a ~$5,000 minimum lump sum; the break-even is usually just a few months of lower payments.
- Weigh liquidity first. Cash tied up in home equity is illiquid and earns only your mortgage rate — keep an emergency buffer before sending funds.
Related calculators
Frequently asked questions
What is a mortgage recast?
A recast (or re-amortization) is when you make a large lump-sum payment toward your principal and the lender recalculates your monthly payment over the same remaining term at the same interest rate. Your rate and payoff date do not change — only the monthly payment drops, because there is less principal to spread across the remaining months.
How much does it cost to recast a mortgage?
Most lenders charge a flat recast fee of roughly $150 to $500 (often around $250). Because the fee is small and fixed, it is almost always recovered within the first few months of lower payments. This calculator shows the exact break-even point and compares the fee against the total interest you save.
What is the minimum lump sum required to recast?
Lenders usually require a minimum principal reduction of $5,000 to $10,000 to recast. Some also require the lump sum to bring your balance below a threshold. If your lump sum is under the typical $5,000 floor, this calculator flags it — check with your servicer for their exact policy before you send funds.
Which loans are eligible for recasting?
Conventional (Fannie Mae / Freddie Mac) and most jumbo loans are eligible. Government-backed loans — FHA, VA and USDA — generally cannot be recast; to lower those payments you would refinance instead. Select your loan type above and the calculator warns you if recasting is unlikely to be available.
Is recasting better than making extra payments?
They serve different goals. A recast lowers your required monthly payment but keeps the original payoff date, so you actually pay slightly more total interest than if you had applied the same lump sum and kept paying the old amount. Applying the lump sum without recasting shortens the term and saves the most interest — but your monthly obligation stays high. To weigh recasting against simply making extra payments, the scenario comparison above shows both paths side by side.
Does recasting lower my interest rate?
No. A recast never changes your interest rate — it only re-spreads a smaller balance over your remaining term. If current market rates are meaningfully lower than your rate, a refinance (which does change the rate, but has larger closing costs) may save more. A recast is best when you like your rate and simply want a lower payment.
Disclaimer: these calculators are educational tools, not financial advice. They model your inputs with published formulas, but they cannot know your full situation — for decisions with real stakes, talk to a qualified professional. Formulas and defaults last reviewed .