Plenty of lenders recast, few do it free, and the math is simply the fee against the payment drop. A recast works like this: you apply a lump sum to your principal balance, and the lender re-amortizes the loan at your same interest rate and remaining term, recalculating the payment against the new, lower balance. Your monthly payment drops, your rate stays put, and you don't requalify the way you would on a refinance. Not every lender offers recasting, so ask yours specifically. In our experience the request rarely gets declined once a lender does offer it. Expect a cost somewhere from a couple hundred dollars up to around $500, since a recast is technically a loan modification that requires new documentation and recording. There's no magic formula beyond weighing that modest fee against how much the payment drops. We had a client pay a roughly $1.9 million mortgage down to about $350,000 after selling a prior home, and recasting the remaining balance was an obvious yes. For a small paydown, the fee may not be worth it. Your servicer can quote the exact cost and the new payment before you commit.