After your first big chunk hits the mortgage, you'll notice something odd. The balance dropped, but the required payment didn't move an inch. Same number, same due date, as if nothing happened.
That's not a mistake. It's how amortized loans work, and for this strategy it's actually the feature. Your payment was calculated from the original balance and term, so when the balance drops and the payment stays fixed, a bigger slice of every payment lands on principal. The chunk keeps paying you back every single month. That's the engine behind why chunking beats dribbling in extra payments psychologically, even though the interest math is the same dollar for dollar.
There's a second lever, though, and it points the other direction: the recast. You make a large principal payment, pay a small processing fee, usually a few hundred dollars, and the lender re-runs the amortization on the new balance over the remaining term. Your required payment drops. Not the rate, not the term, just the monthly obligation.
So which do you want? Depends on which number you're solving for. If the goal is payoff speed, don't recast. Keep the payment high and let the principal share snowball. If the goal is breathing room, because income dropped or the budget runs tight, a recast converts your chunk into permanent monthly relief without refinancing or touching your rate. Some households do both over time: chunk for years, then recast once late in the game when cash flow matters more than speed.
Not every loan can be recast. Government-backed loans often can't, some servicers set minimum principal amounts, and a few just don't offer it. One phone call to your servicer settles it. Ask before you need the answer, and file it next to your monthly review notes as one more tool on the bench.