Mortgage rates are moving below 4 percent for 30-year fixed conforming loans with balances below $417,000 for the first time since they spiked in June 2013. It's not a huge move by the numbers, but psychologically it could be a major boost—potentially prompting a leap of faith for home buyers, but more likely a push for those looking to refinance existing loans.

"Rates have been under a bit of pressure so far this morning," Mortgage News Daily's Matthew Graham said Tuesday. "The first few rate sheets are right on the edge of 3.875 percent. Four percent would still be significantly more prevalent today, but 3.875 percent is out there for a few lenders."