Key Takeaways
- A mortgage recast typically costs $150 to $500 in lender fees. A refinance costs 2% to 5% of the loan balance, or $6,000 to $15,000 on a $300,000 balance.
- Refinancing at the wrong time resets your amortization clock and adds years of front-loaded interest. On a $400,000 loan, that mistake can cost $40,000 or more in total interest paid.
- Run the recast math first: divide your lump-sum paydown by the remaining loan balance, multiply by your current monthly principal-and-interest payment, and compare the result to a refinance's break-even timeline before you call your lender.
- Tool: Calculate your recast savings with the CalcMoney Mortgage Calculator →
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What a Mortgage Recast Actually Is
A mortgage recast is a lender-approved reamortization of your existing loan after a lump-sum principal payment. Your rate, term, and loan servicer stay identical. The lender recalculates your monthly payment using the reduced principal balance spread across your remaining term.
No new loan. No credit inquiry. No appraisal. Most conventional loans serviced by Fannie Mae or Freddie Mac are eligible. FHA loans, VA loans, and USDA loans are not.
Minimum lump-sum requirements vary by lender but typically run between $5,000 and $10,000. The administrative fee runs $150 to $500.
The Core Recast Calculation
The new monthly payment after a recast follows standard amortization math. Write it out as plain arithmetic:
New Monthly Payment = Remaining Balance After Paydown x (Monthly Rate x (1 + Monthly Rate) ^ Remaining Months) / ((1 + Monthly Rate) ^ Remaining Months - 1)
Where Monthly Rate = Annual Interest Rate / 12.
You do not need to solve that by hand. The CalcMoney Mortgage Calculator accepts a revised principal balance and produces the new payment instantly. What matters is understanding the three inputs that drive the result: the paydown amount, the remaining term, and your current rate.
Worked Example 1: The $50,000 Lump Sum on a 30-Year Loan
Starting position. A homeowner took out a $450,000 30-year fixed mortgage at 6.75% seven years ago. The current remaining balance is $408,200. The current principal-and-interest payment is $2,919 per month.
Recast scenario. The homeowner applies a $50,000 lump sum, reducing the balance to $358,200. The remaining term is 276 months (23 years). At 6.75% annual rate, the monthly rate is 0.5625%.
Plugging into the formula:
New Monthly Payment = 358,200 x (0.005625 x (1.005625)^276) / ((1.005625)^276 - 1)
New Monthly Payment = $2,562
Monthly savings: $2,919 - $2,562 = $357 per month.
Total interest paid over the remaining 276 months at the new payment: approximately $349,100. Without the recast, total remaining interest would have been approximately $398,900. Interest savings: $49,800.
Recast fee: $350. Net benefit: $49,450.
Worked Example 2: Refinancing the Same Loan
Same starting position. $408,200 balance, 276 months remaining, current rate 6.75%.
Refinance scenario. Current market rates for a 30-year fixed mortgage are 6.40%. The homeowner refinances into a new 30-year loan at 6.40% with $8,164 in closing costs (2% of the new balance, rolled in, bringing the new loan to $416,364).
New monthly payment at 6.40% on $416,364 over 360 months: $2,601.
Monthly savings versus the original payment: $2,919 - $2,601 = $318 per month.
Break-even on closing costs: $8,164 / $318 = 25.7 months, or just over two years.
Total interest paid over 360 months at 6.40% on $416,364: approximately $520,200.
Compare that to the recast: $349,100 in remaining interest paid over 276 months.
The refinance produces a lower monthly payment ($2,601 vs. $2,562 is close, but note the recast actually wins here by $39/month), and it extends the loan by 84 months. Over those extra 84 months, the homeowner pays an additional $218,500 in interest that the recast timeline never incurs.
Conclusion on Example 2. The refinance wins only if the homeowner plans to sell within the break-even window or if rates drop substantially further, say to 5.75% or below, where the interest-rate delta overwhelms the term extension penalty.
When Refinancing Beats a Recast
Refinancing produces a better long-term outcome under three specific conditions.
First: The rate differential exceeds 1.25 percentage points. A drop from 7.25% to 5.875% generates enough monthly savings to offset closing costs and the amortization reset within a reasonable hold period.
Second: The homeowner intends to stay in the property fewer than four years. The monthly savings from a lower rate can exceed the cost of closing over a short horizon, whereas the recast's value compounds over a longer remaining term.
Third: The current loan carries private mortgage insurance. A refinance can eliminate PMI if the new loan-to-value ratio falls below 80%, a structural savings that a recast cannot generate on its own.
When a Recast Wins Clearly
The recast is the correct choice when the current rate is already competitive, the homeowner holds a lump sum from a bonus, inheritance, or property sale, and the remaining term is long enough for reamortization to generate material interest savings.
It also wins when credit has deteriorated since the original loan. A refinance at a worse rate than the existing mortgage is almost never rational. A recast preserves the original rate unconditionally.
The Break-Even Comparison Framework
Before calling a lender, run this three-step comparison.
Step 1. Calculate the new recast payment using the formula above or the CalcMoney Mortgage Calculator. Subtract it from your current payment to get the monthly savings. Multiply by the remaining months to get gross interest savings. Subtract the recast fee.
Step 2. Get a refinance quote from at least two lenders. Credible allows side-by-side rate comparison with real prequalified offers. Calculate the new payment, identify closing costs, and divide closing costs by monthly savings to get the break-even month.
Step 3. Compare total interest paid across both paths using the same remaining horizon. Use your planned hold period as the cutoff, not the full loan term.
If the recast's total interest cost over your hold period is lower than the refinance's total interest cost over the same period, the recast wins. If the refinance break-even lands inside 24 months and the rate drop exceeds 1 percentage point, the refinance likely wins.
Run Your Own Numbers Before You Commit
The worked examples above use specific loan sizes and rates. Your balance, rate, paydown amount, and local closing cost environment will produce a different result.
The CalcMoney Mortgage Calculator accepts your exact remaining balance, current rate, remaining term, and proposed lump sum. It outputs the new payment, total interest saved, and a comparison against a refinance scenario at any rate you specify. Run both scenarios before contacting your servicer or a new lender. The math takes three minutes. The wrong decision costs tens of thousands.
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Results are estimates for informational purposes only. Consult a licensed financial professional before making financial decisions.
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