Mortgage Recast Calculator
Made a big lump-sum payment toward your mortgage? See your new, lower monthly payment after a recast (also called a re-amortization) — same interest rate, same remaining term — plus how much you'll save each month and in total interest.
A recast re-amortizes your remaining balance over the same term at the same rate after a lump-sum principal payment, lowering the monthly payment. Pay $50,000 toward a $300,000 balance at 6.5% with 25 years left and the payment drops from about $2,025.62 to about $1,688.02 a month — saving roughly $337.60/mo. Your rate and payoff date don't change; only the payment does.
Enter your numbers
New to this? Leave the defaults — they're realistic — and just change your balance, rate and lump sum.
How to use this calculator
- Enter your current loan balance — the principal you still owe today, which you can find on your latest mortgage statement.
- Enter your interest rate exactly as it is now. A recast doesn't change it.
- Enter the years remaining on the loan, not the original term.
- Enter the lump sum you plan to pay toward principal before the recast.
- Adjust the recast fee if your lender's differs from the $250 default. Your new monthly payment, monthly savings and total interest saved update instantly.
How a mortgage recast works
A recast (sometimes called a "re-amortization") lets you lower your monthly mortgage payment by paying a large chunk of principal up front. You give the lender a lump sum, they apply it to your balance, and then they recalculate — or re-amortize — your payment so the smaller balance is paid off over your same remaining term at your same interest rate. The result is a lower required payment every month for the rest of the loan.
The key thing to understand is what doesn't change. Your interest rate stays put. Your payoff date stays put. You keep the exact same loan — there's no new application, no credit check and no appraisal. The only number that moves is the monthly payment, because the lender is now spreading a smaller principal across the same number of months.
This makes a recast fundamentally different from a refinance. A refinance swaps your loan for a brand-new one, which can lower your rate but comes with closing costs that often run thousands of dollars. A recast usually costs just a small flat fee — typically $150 to $500 — and is done in a few weeks. The trade-off is that a recast can never lower your rate; it only restructures the payment on the balance you already have.
Recasting also differs from simply making an extra principal payment. If you pay extra without recasting, your monthly payment stays the same and the loan just gets paid off sooner. If you recast, the loan still ends on the original date, but each monthly payment is smaller — trading a faster payoff for more breathing room in your monthly budget.
The formula & how we calculate it
Both your old and new payments come from the standard amortizing-loan payment formula. The trick to a recast is that we run the formula twice with the same rate and the same number of months — once on the old balance, once on the balance after your lump sum.
P = principal (balance before, then after the lump sum)
r = monthly interest rate = rate ÷ 12 ÷ 100
n = months remaining = years × 12
Worked example (the defaults above):
- Current balance
P= $300,000, rate 6.5% sor= 0.0054167, term 25 years son= 300 months. - Old payment = amortize($300,000) ≈ $2,025.62 / month.
- Lump sum of $50,000 brings the new principal to $250,000.
- New payment = amortize($250,000) over the same 300 months at 6.5% ≈ $1,688.02 / month.
- Monthly savings = $2,025.62 − $1,688.02 = $337.60 / month.
- Total interest falls from about $307,686 to about $256,405 — a saving of roughly $51,281 over the life of the loan (before the $250 recast fee).
If the rate were 0% (rare for a mortgage), the formula simply becomes the balance divided by the number of months, since there's no interest to add.
What affects your recast result
- Size of the lump sum. The bigger the principal payment, the lower your new payment and the more interest you save. This is the single biggest lever.
- Your interest rate. A higher rate means each dollar of principal you knock off saves more interest — so recasting tends to be more powerful on higher-rate loans.
- Years remaining. Recasting earlier in the loan spreads the savings over more months, magnifying the total interest you avoid. Late in a loan there's less interest left to save.
- The recast fee. A small flat fee (often $150–$500) barely dents the savings, but it's worth confirming with your lender along with any minimum lump-sum requirement.
- Loan eligibility. Conventional loans usually allow recasting; FHA, VA and USDA loans generally do not. Jumbo and some investor loans have their own rules.
Frequently asked questions
What is a mortgage recast?
A mortgage recast is when you make a large lump-sum payment toward your loan's principal and the lender re-amortizes the remaining balance over your same remaining term at your same interest rate, producing a lower monthly payment. Unlike refinancing, you keep your existing loan, rate and payoff date — only the monthly amount changes. For example, paying $50,000 toward a $300,000 balance at 6.5% with 25 years left drops the payment from about $2,025.62 to about $1,688.02 a month.
What's the difference between a recast and a refinance?
A recast keeps your existing loan, interest rate and remaining term and simply lowers the payment after a lump-sum principal payment. A refinance replaces your loan entirely with a new one — a new rate, a new term and a full round of closing costs (often 2%–5% of the balance). A recast usually costs only a small flat fee (about $150–$500), requires no credit check or appraisal, and is far faster. The trade-off: a recast can't lower your rate, while a refinance can.
Does recasting lower my interest rate?
No. A recast does not change your interest rate — it stays exactly the same, and so does your remaining term. The only thing that changes is your monthly payment, which drops because the lender re-amortizes a smaller balance over the same number of months. You still save on total interest, but that comes from owing less principal, not from a lower rate. If lowering your rate is the goal, you'd need to refinance instead.
How much does a mortgage recast cost?
Recasting is cheap compared with refinancing. Most lenders charge a one-time flat fee of roughly $150 to $500 — no closing costs, no appraisal, no credit check. Many lenders also require a minimum lump-sum payment (commonly $5,000–$10,000) before they'll re-amortize, and not every loan is eligible — FHA, VA and USDA loans generally cannot be recast. Always confirm your lender's fee and minimum before sending the money.
Is recasting worth it?
Recasting is worth considering if you have a lump sum, like your current rate, and want a lower required monthly payment without the cost and hassle of refinancing. It frees up monthly cash flow and saves total interest for a small flat fee. The downsides: it ties up cash in home equity you can't easily get back, and it won't shorten your payoff date or lower your rate. If you'd rather be debt-free sooner, making extra principal payments without recasting keeps your payment the same but pays the loan off faster.