No reason to wait. Every extra dollar toward principal stops accruing interest the day it's applied. The mechanics are simple. At an illustrative 5.7% rate, an extra $100 of principal saves about $5.70 in interest over the following year, and because the balance is permanently lower, it keeps saving in every year after that. Make it a monthly habit and the effect builds on itself, shaving real time and interest off the loan with no refinance required. Waiting until you refinance just leaves those dollars idle against the mortgage in the meantime. The one caution is liquidity. Money you put into the home is illiquid; getting it back out means a cash-out refinance or a second mortgage, which is slower and more expensive than simply having kept the cash. So fund your emergency reserves first, then send extra to principal from whatever is comfortably left over. Prepaying and refinancing also aren't either-or. Pay extra now, and if you refinance later, the smaller balance carries straight into the new loan.