Capital structure
A lump sum against a legacy note rate: what it buys in monthly relief, and what a refinance would cost instead.
Monthly relief
Computed
The loan
From your latest statement, not the original note amount.
The rate you locked. A recast does not touch it.
Payment number to the payoff date, divided by twelve if you only know years.
Recasts exist on conventional conforming loans. FHA, VA and USDA do not allow them.
The move
Curtailment, not prepayment: the servicer re-amortizes instead of shortening the term.
Typically $150 to $500, flat, with no appraisal and no underwriting.
The inverse of the headline: the engine solves for the lump sum that buys this.
The recast, line by line
The refinance, priced
Deploying the same $50,000 at 4.0% for 10 years grows by $24,012 before tax. Curtailing it returns $18,845 over the same window, tax-free, because it is interest you never pay.
Read before calling the servicer
Market rate and closing-cost share are defaults you can overwrite. Everything else is arithmetic on your own figures.
A recast re-amortizes the balance you already have over the months you already owe, at the rate you already locked. So the payment relief is set by one number — how much principal you retire — and it does not matter whether your statement is a month stale.
A servicer charges a flat administrative fee, usually $150 to $500. There is no appraisal, no title work, no income verification and no credit pull, which is why the fee returns in weeks rather than years.
Liquidity, and any return that cash would have earned. The engine prices that as the interest you no longer pay, which is a guaranteed return at your note rate and is not taxed. Compare it against what the same money earns elsewhere before deciding.
M_recast = P_new [ r(1+r)^n / ((1+r)^n − 1) ]
relief = (P_before − P_new) × paymentFactor(r, n)
payback (months) = servicer fee / relief
rate to match = solve PMT(balance, r30, 360) = M_recast
interest avoided = relief × months remaining
Conforming limits are the 2026 FHFA baseline for a one-unit property. High-cost counties are not modelled here; if your loan is near the line, ask the servicer for the limit that applies to your county.