Freddie Mac said the average interest rates for 30-year, fixed-rate loans fell under 4 percent for the first time, dropping to 3.94 percent with an average of 0.8 points for the week.
A week earlier, the rate hovered just above 4 percent at 4.01 percent. A year ago during the same week of the year, the rates averaged 4.27 percent.
For 15-year loans, the rate dropped to a historic low for the sixth consecutive week, dropping to 3.26 percent, down from 3.28 percent last week and from 3.72 percent a year earlier.
Frank Nothaft, Freddie Mac's vice president and chief economist, said long-term rates fell as the U.S. Federal Reserve began a program of replacing $400 billion in short-term treasury securities with long-term bonds, a plan designed to push long-term rates lower.