Point your extra dollars at the higher-rate debt and leave the ultra-low-rate loan alone. When you hold two mortgages at very different rates, the higher-rate loan is where each dollar works hardest. Using round, illustrative numbers: if the kept home carries a rate near 2.375% and the new home would be around 6%, a dollar aimed at the 6% loan saves far more interest than a dollar aimed at the sub-3% loan. A very low fixed rate is close to the cheapest money you'll ever borrow, and there's little reason to rush to retire it. A home you've held a while has usually built a solid equity cushion already, so the newer, higher-rate loan is the one that needs the attention. One honest caveat: that's the math on rate alone. The full answer also depends on: - Liquidity. The cash cushion you keep can matter more than the interest you shave. - Whether the first home becomes a rental producing income. - Your tax picture. Worth a conversation with a tax professional before you move a large sum. We'd run your actual numbers before committing either way. That's what the free Roadmap conversation (about 20 minutes) is for.