The 60-second rule
The recast wins the default duel — by $11,595.74. Current path: $2,453.17/mo, $444,826.49 total interest over 27 years. Refinance at 6.4% for 27 years: $2,272.15/mo ($181.02 lower), $386,175.59 total interest — net savings $51,650.90 after $7,000 in closing costs, break-even in 38.7 months. Recast with $50,000 ($300 fee): $2,102.72/mo ($350.45 lower), $381,279.85 total interest — net savings $63,246.64. Default check: $63,246.64 − $51,650.90 = $11,595.74 to the recast. But the $50,000 invested at 7% for 27 years grows to $310,693.38 — a $260,693.38 gain that dwarfs both mortgage branches.
The worked example, line by line
Setup: $350,000 balance, 27 years (324 payments) remaining, current rate 7.2%; refi at 6.4% for 27 years with $7,000 closing costs; recast with a $50,000 lump sum and a $300 fee; invest-at-7% branch for the lump sum.
Line 1 — the current leg. Monthly rate = 7.2% ÷ 12 = 0.006. Payment = $350,000 × 0.006 ÷ (1 − 1.006−324) = $2,453.17. Total paid = $2,453.17 × 324 = $795,826.49; minus the $350,000 balance = $444,826.49 total interest.
Line 2 — the refinance leg. Monthly rate = 6.4% ÷ 12. Payment = $350,000 × 0.005333… ÷ (1 − 1.005333…−324) = $2,272.15. Monthly drop = $181.02. Total interest = $386,175.59. Net savings vs current = $444,826.49 − $386,175.59 − $7,000 costs = $51,650.90. Break-even = $7,000 ÷ $181.02 = 38.7 months.
Line 3 — the recast leg. New balance = $350,000 − $50,000 = $300,000, same 7.2% rate and 324 payments. Payment = $2,102.72. Monthly drop = $350.45. Total interest = $381,279.85. Net savings = $444,826.49 − $381,279.85 − $300 fee = $63,246.64.
Line 4 — the verdict. $63,246.64 − $51,650.90 = $11,595.74 to the recast. It wins on both axes: the bigger monthly drop ($350.45 vs $181.02) and the bigger lifetime savings.
Line 5 — the invest-it branch. $50,000 at 7% for 27 years = $50,000 × 1.0727 = $310,693.38, a $260,693.38 gain. Neither mortgage branch comes within an order of magnitude — which is why the invest-vs-pay-down question deserves its own line, not a footnote.
Branch — the bigger rate drop (5.4%): refi payment = $2,054.70, monthly drop $398.47, break-even = $7,000 ÷ $398.47 = 17.6 months. A bigger rate gap compresses the break-even below the 5-year move horizon and the refinance pulls even with the recast.
Branch — no lump sum: the recast branch switches off entirely — there is no recast without a lump sum. The refinance stands alone at $51,650.90 net savings; the only remaining question is whether the 38.7-month break-even survives your move date.
Branch — the 15-year refi: payment = $3,029.67 — $576.50 more than your current payment, not less. Total interest collapses to $195,340.23; net savings = $444,826.49 − $195,340.23 − $7,000 = $242,486.27. It is a savings machine that demands a bigger check every month — affordability, not arithmetic, decides this branch.
Branch — $12,000 closing costs: break-even stretches to $12,000 ÷ $181.02 = 66.3 months — past the 5-year move horizon. Move-date check at 5 years: refinance nets $3,861.28 ($181.02 × 60 − $7,000) while the recast nets $20,727.16 ($350.45 × 60 − $300). With a 5-year move date, the recast’s cheap entry fee is the whole ballgame.
Branch — investing at 10%: $50,000 × 1.1027 = $655,499.71. Compounding at 10% leaves both mortgage branches in the dust — but 10% nominal for 27 straight years is a hope, not a plan, which is why the default stays at 7%.
Output · formula · meaning
| Output | Formula | What it means |
|---|
| Refinance monthly payment | balance × r ÷ (1 − (1+r)−n) | $2,272.15 at the defaults — the new check you write every month after the rate resets to 6.4%. |
| Recast monthly payment | (balance − lump) × r ÷ (1 − (1+r)−n) | $2,102.72 at the defaults — same rate and term, recomputed on the $300,000 post-lump balance. |
| Net savings vs current path | current total interest − branch total interest − branch cost | $51,650.90 refi, $63,246.64 recast — the only number that nets the savings against what each branch costs to enter. |
| Refinance break-even | closing costs ÷ monthly payment drop | 38.7 months at the defaults — how long you must stay before the refi has paid for itself. Moving sooner turns it into a loss. |
| Invest-the-lump future value | lump × (1 + return)years | $310,693.38 at 7% for 27 years — what the recast’s lump sum becomes if it goes to the market instead. |
Who uses this
- The rate-watcher with a windfall: a $50,000 bonus lands while rates have fallen 0.8 points — runs the duel and learns the recast saves $63,246.64 vs the refi’s $51,650.90, a $11,595.74 gap, before calling the servicer.
- The 5-year mover: runs the move-date check and sees the refi nets only $3,861.28 over 5 years against $7,000 in costs — and picks the recast ($20,727.16) or does nothing at all.
- The shorten-the-term shopper: runs the 15-year branch and learns it saves $242,486.27 while raising the payment $576.50 — then stress-tests the budget against the bigger check.
- The invest-vs-pay-down debater: runs the invest-it branch — $310,693.38 at 7% — and gets an honest side-by-side instead of a slogan, with the 10% preset showing $655,499.71 when markets cooperate.
Accuracy & limitations
The amortization math is exact: every payment uses the standard fixed-rate formula, and total interest is payment × months − balance on each branch. The model is fixed-rate only — ARMs, interest-only, and balloon loans don’t fit. Taxes, insurance, HOA, and PMI are unchanged on both branches and excluded from every figure, so these are principal-and-interest savings, not escrow totals. Recast availability varies by servicer and loan type — most conventional servicers allow recasts for a $0–500 fee, but FHA and VA loans are generally ineligible, and some loans require a minimum lump sum (often $5,000–10,000) or a seasoning period. The invest-it branch compounds the lump sum annually at your assumed return — a model, not a market forecast. This is a comparison calculator, not mortgage advice.
Cite this calculatorBright Side Kit. “Refinance vs Recast: Which Mortgage Move Saves More? | Bright Side Kit.”
brightoolbox.com, 2026.
Bright Side Kit. "Refinance vs Recast: Which Mortgage Move Saves More? | Bright Side Kit." https://brightoolbox.com/refinance-vs-recast/ Accessed October 24, 2026.Data sources- Standard fixed-rate amortization formula — payment = P × r ÷ (1 − (1+r)−n), computed with monthly compounding on every branch.
- Mortgage recast (re-amortization) conventions — lump-sum principal reduction followed by payment recomputation at the same rate and term; servicer fees typically $0–500; FHA/VA loans generally ineligible.
- Freddie Mac Primary Mortgage Market Survey context — the 7.2% → 6.4% rate gap reflects the 2024–2025 fixed-rate landscape the defaults are built on.
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Frequently asked questions
What is the difference between refinancing and recasting a mortgage?
Refinancing replaces your loan; recasting keeps it and redoes the math. A refinance pays off the old mortgage with a brand-new loan at a new rate, term, and closing-cost bill — $7,000 in this page’s model. A recast (re-amortization) keeps your current loan, rate, and term: you pay a $50,000 lump sum, the servicer recomputes the payment on the $300,000 balance for a $300 fee. Same house, same rate, smaller check.
Is it better to refinance or recast?
At the page’s defaults, the recast wins by $11,595.74 — it saves $63,246.64 vs the refi’s $51,650.90, with the bigger monthly drop ($350.45 vs $181.02). But you need the $50,000 lump sum, your servicer must allow recasts, and a bigger rate drop (try the 5.4% preset) tilts the duel toward the refinance. Run your numbers — the winner moves with the rate gap and the lump sum.
How do you calculate the break-even point on a refinance?
Closing costs ÷ monthly savings. $7,000 ÷ $181.02 = 38.7 months — you must keep the loan about 3.2 years before the refinance has paid for itself. Sell or refinance again sooner and you lose money on the deal. The $12,000-costs preset stretches it to 66.3 months.
Can I recast an FHA or VA loan?
Usually not. Most conventional-loan servicers offer recasts for a $0–500 fee, but FHA and VA loans are generally ineligible — their program rules don’t include re-amortization. Some servicers also require a minimum lump sum ($5,000–10,000) or a seasoning period. Call your servicer and ask for “recast” or “re-amortization” before counting on it.
Should I recast or invest the lump sum?
The math favors investing — the risk favors the recast. $50,000 at 7% for 27 years grows to $310,693.38 (a $260,693.38 gain), far above the recast’s $63,246.64 interest savings. But the market return is a hope and the mortgage savings are a lock: the recast’s $350.45 monthly drop is guaranteed, the 7% is not. Pick the guaranteed floor, the expected ceiling, or split the lump sum between both.
Does recasting shorten the loan term?
No — that’s the point. A recast keeps your 27-year remaining term and your rate; it only recomputes the payment on the lower balance. If you want a shorter term, you’re looking at a refinance (the 15-year branch saves $242,486.27 in interest) or just paying extra each month.
What if I plan to move in 5 years?
The cheap entry fee wins. Over 5 years the refinance nets $3,861.28 ($181.02 × 60 − $7,000) while the recast nets $20,727.16 ($350.45 × 60 − $300). A 38.7-month break-even barely clears a 5-year horizon — and a 66.3-month one doesn’t clear it at all. Short time horizon? Recast or sit tight.