The choice lenders rarely volunteer
A recast is the quiet option: a few hundred dollars, same rate, same payoff date, lower payment — but only some loans allow it, and most government-backed loans do not. A refinance resets everything and costs thousands up front, which only pays off if the rate drop is big enough and you stay long enough. The verdict above does that math instead of guessing.
Recasting shines in one specific situation: your existing rate is lower than what a refinance would get you today, and what you want from the windfall is a smaller required payment. The lender takes your lump sum, re-runs the amortization on the smaller balance over the months you already had, and charges a processing fee that's typically a few hundred dollars — no appraisal, no closing, no credit pull, no rate roulette. Your below-market rate survives untouched, which is exactly why nobody upstream is eager to suggest it.
The eligibility fine print: FHA, VA, and USDA loans generally can't be recast at all, and lenders that do allow it usually want a meaningful minimum principal payment (often $5,000–$10,000) and a loan that's current. Conventional conforming loans are the usual candidates. One phone call to your servicer — "do you offer recasting, what's the fee, what's the minimum" — settles it in five minutes.
And there's a third door the comparison above doesn't need a button for: just pay the lump sum toward principal and don't recast. Your required payment stays the same, so instead of payment relief you get a shorter loan and less lifetime interest — often the cheapest outcome of the three if cash flow isn't the problem you're solving. Our mortgage payoff calculator shows exactly what that version buys. Refinancing earns its closing costs only when the rate drop is large and your stay is long — which is precisely what the break-even line in the verdict is checking.