Separate two questions that feel like one: must you touch the low-rate loan at all, and if so, is the move worth it. If you are keeping the current home and just need cash from it, you may never have to disturb the low first mortgage. A second mortgage or HELOC pulls equity while leaving the first loan in place, so the higher rate applies only to the new money. That is often the cleanest way to protect a rate around, illustratively, 3 percent while still funding the next down payment. If you are selling the current home to buy the next one, the low rate goes away regardless, and the real question becomes whether the move is worth it to you. The numbers are only part of that answer. Jeb lived this exact call: about five years in, he gave up a roughly 3 percent rate because his family had outgrown the house, and a few months later he was glad he did, higher payment and all. Life fit can outweigh a rate. Either way, have a lender quantify precisely what you would be giving up before you commit, so the decision runs on real figures instead of fear of losing the rate. One caution: a big national builder's in-house lender may not walk you through that tradeoff carefully, so get a second set of eyes. Running keep-and-borrow against sell-and-move is exactly what the free Roadmap conversation is for.