Mortgage Recast Calculator

Free Mortgage Recast Calculator Online – Lower Your Monthly Payment With a Lump Sum

Most homeowners who come into a windfall — a bonus, an inheritance, proceeds from a property sale — face the same fork in the road: put it toward the mortgage or invest it elsewhere. What almost nobody mentions in that conversation is a third option that sits quietly between the two: a mortgage recast. It keeps the same loan, same interest rate, same lender — but uses a lump sum to permanently reduce the monthly payment going forward. No credit check, no application process, and none of the closing costs that come with refinancing. Bluxe’s free online mortgage recast calculator shows you exactly what that monthly reduction looks like and how much total interest you’d save, before you ever contact your lender.

What Is a Mortgage Recast?

A mortgage recast — sometimes called a loan re-amortization — is a process where a homeowner makes a large one-time payment toward the principal balance, and the lender then recalculates the monthly payment based on the new, lower balance. The original interest rate and remaining loan term stay exactly the same. Only the payment amount changes, spreading the reduced balance across the remaining months at a lower monthly figure.

What makes recasting meaningfully different from simply making an extra payment is that extra payments alone don’t lower your required monthly obligation. They reduce your balance and shorten the loan term, but your minimum payment stays unchanged until the loan ends. A recast does the opposite — it keeps the loan term intact but permanently lowers the payment you’re contractually required to make each month. That monthly breathing room is what makes recasting attractive for people who want reduced cash flow obligations rather than a faster payoff. Most lenders charge a modest administrative fee for the process, typically between $150 and $500, which is far less than the thousands refinancing costs — and there’s no rate risk since your existing rate is locked in.

How Does This Calculator Work?

The recast calculation runs two amortization schedules in parallel: one based on your current balance before the lump sum, and one based on the reduced balance afterward. Both use the same remaining term and interest rate.

Step 1 — Establish the Current Monthly Payment

Using the standard amortization formula applied to the current principal balance and remaining term:

M = B × [r(1+r)^n] ÷ [(1+r)^n − 1]

Where B is the current principal balance, r is the monthly interest rate (annual rate ÷ 12), and n is the remaining number of monthly payments.

Worked example: Current balance $250,000, rate 4.5%, 25 years remaining.

r = 0.045 ÷ 12 = 0.00375 n = 25 × 12 = 300 (1.00375)^300 = 3.0748 M = 250,000 × [0.00375 × 3.0748] ÷ [3.0748 − 1] M = 250,000 × 0.011531 ÷ 2.0748 = $1,389.35 per month

Step 2 — Apply the Lump Sum and Calculate New Balance

New Principal = Current Balance − Lump Sum Payment

Example: $250,000 − $50,000 = $200,000

Step 3 — Recast the Payment on the New Balance

The same formula is applied to the new principal, keeping n and r identical:

M (recast) = 200,000 × [0.00375 × 3.0748] ÷ [3.0748 − 1] = $1,111.48 per month

Monthly Saving = $1,389.35 − $1,111.48 = $277.87

Step 4 — Calculate Total Interest Savings

Total Interest (Before Recast) = (M × n) − Current Balance Total Interest (After Recast) = (M recast × n) − New Balance Interest Saved = Difference between the two totals

Figures based on: $250,000 current balance, 4.5% rate, 25 years remaining.

How to Use the Calculator on Bluxe

1. Open the Mortgage Recast Calculator on Bluxe and enter your original loan amount — the total amount borrowed when the mortgage was first taken out, before any payments were made.
2. Enter your current principal balance — this is the outstanding amount you owe today, found on your most recent mortgage statement; it should be less than the original loan amount.
3. Type your interest rate as a percentage — use your actual loan rate from your mortgage agreement, not a market estimate, since the recast keeps your existing rate in place.
4. Enter your original loan term in years — typically 15, 20, or 30 years depending on your mortgage structure.
5. Enter the time remaining on your loan in years — if you’re 7 years into a 30-year mortgage, enter 23. Practical tip: if your remaining time doesn’t fall on a clean year boundary, use a decimal — 22.5 for 22 years and 6 months — as this improves the accuracy of the payment projections.
6. Enter the lump sum you’re considering for the recast — this is the extra principal payment you’d make before requesting the recast from your lender.
7. Click “Calculate Recast” to generate your full results: monthly payment before and after, monthly saving, total interest before and after, and total saving across the remaining loan term.
8. Switch between the Summary tab for an overview and the Amortization tab for a full month-by-month or year-by-year comparison of the two repayment schedules.

Understanding Your Results

The results are organized across two panels — a headline summary and a detailed amortization comparison — each serving a distinct purpose.

The Monthly Payment Savings panel shows your before and after payment side by side, the dollar reduction, and the percentage reduction. This is the figure most relevant to your monthly budget — it’s a permanent reduction in your required payment for the remainder of the loan.

The Total Interest Savings panel shows how much less interest you’d pay across the remaining term in total. The lump sum doesn’t just reduce today’s payment; because interest accrues on the outstanding balance every month, a lower starting balance after recast means lower interest charges on every single subsequent payment across what could be decades.

The Amortization Schedule comparison is where the mathematical reality becomes tangible — you can see, month by month or year by year, how the two trajectories diverge from the point of recast onward.

Why This Matters

Refinancing gets most of the attention when homeowners want to lower their mortgage payment, but it comes with a cost that often goes underappreciated in the calculation. Closing costs on a refinance typically run between 2% and 5% of the loan amount — on a $300,000 mortgage, that’s $6,000 to $15,000 in fees, paid upfront, before any monthly savings begin to accumulate. The break-even period on those costs can stretch to three to five years, which matters enormously for anyone who might sell or relocate before then.

A recast sidesteps all of that. For homeowners who received a lump sum — perhaps from selling a previous property during a move-up purchase, or from a multi-year investment maturing — and want to reduce their monthly obligations without resetting their loan term or paying closing costs, recasting is the cleaner option. The administrative fee is fixed and small, the interest rate stays exactly where it is, and the reduction in monthly payment takes effect immediately after the recast is processed. That simplicity is genuinely valuable in a financial landscape where most mortgage options involve trade-offs measured in thousands of dollars and years of payback periods.

Practical Tips

Confirm your lender offers recasting before planning around it Not all lenders offer mortgage recasting — government-backed loans such as FHA and VA loans typically don’t qualify, and some conventional lenders don’t offer the option at all. Jumbo loans are often recasted. Before directing a lump sum toward a planned recast, call your lender and confirm both eligibility and the administrative fee. The calculator’s projections are accurate once those conditions are confirmed.

Compare recast savings against investing the lump sum A $50,000 lump sum used for a recast might save you $277 per month and $83,000 in total interest. That same $50,000 invested at a 7% average annual return over 25 years would grow to approximately $271,000. The right choice depends on your mortgage rate, your investment risk tolerance, tax situation, and how much you value the monthly cash flow reduction. The calculator gives you the mortgage side of that comparison precisely; the investment side requires separate modelling.

Time the recast strategically if you’re early in the loan Because mortgage interest is front-loaded — the earliest payments are overwhelmingly interest — a recast executed in the first five to ten years of a 30-year loan produces greater total interest savings than the same recast done later. The new, lower balance is charged interest across a longer remaining period, which multiplies the saving. Homeowners who receive a windfall early in their loan life should factor this timing advantage into the decision.

Keep the monthly saving working for you The reduced monthly payment from a recast frees up cash — but that cash only benefits you if it’s redirected deliberately. Letting the $277 monthly saving disappear into general spending produces no lasting financial benefit. Channeling it into an investment account, an emergency fund, or additional mortgage overpayments gives the recast a compounding return beyond just the interest saving it directly generates.

Run the calculation before and after a potential interest rate change If you’re considering recasting but also watching market rates in case refinancing becomes attractive, model both scenarios side by side. A recast at your current rate might save $250 per month; refinancing to a rate one percentage point lower might save $300 per month — but with $8,000 in closing costs and a 2.7-year break-even period. The calculator gives you the recast side of that comparison with precision.

Who Should Use This Calculator?

Any homeowner with a lump sum available and a desire to reduce monthly obligations without the cost or complexity of refinancing. More specifically:

• Homeowners who’ve recently sold a previous property and are applying equity to a new purchase, wanting to model the payment reduction that would result from directing remaining proceeds into a recast
• People who received an inheritance, bonus, or investment payout and are deciding between paying down the mortgage, investing, or some combination of both
• Move-up buyers who ported an existing mortgage and want to lower the payment by applying surplus funds from the sale without resetting their loan term
• Households anticipating an income reduction — a planned career change, retirement transition, or a partner stopping work — who want to permanently lower their fixed monthly housing cost before income drops
• Anyone comparing a recast against refinancing who needs the precise monthly saving and total interest reduction from the recast option to make the comparison fairly

If you found this helpful, you might also want to try Bluxe’s [Karl’s Mortgage Calculator] to get a fuller picture.

A note before you go — the projections this calculator produces are based on fixed inputs and assume the lump sum reduces principal immediately before re-amortization, which is how recasting works in practice. Results don’t include the lender’s administrative recast fee, potential prepayment penalties, or variations in how individual lenders process the recast timeline. Always confirm the exact terms and process with your lender before committing funds. For decisions involving large lump sums and long-term financial planning, a qualified mortgage adviser or financial planner should be part of the conversation.