The 15-year fixed rate fell to 2.56% from 2.61%. A year ago, it stood at 3.07.
The most popular mortgage, the 30-year fixed rate, came in at 3.35%, a drop of 0.05 percentage point and only 0.04 percentage point above its record low set the week of November 21, 2012.
The rates provide a welcome boost to the housing market and to the overall economy, according to Frank Nothaft, Freddie Mac's chief economist.
"Residential fixed investment added to overall economic growth over the past eight consecutive quarters and contributed more than 0.3 percentage points in growth over the first three months of this year," he said. "[N]ear record low mortgage rates should further drive the housing market recovery over the near term."
The news came a day after the Fed announced that it would keep buying up to $85 billion in mortgage-backed securities and Treasuries a month.
"There was a chance that the Fed would start to taper their purchases as summer approached," said Keith Gumbinger, of HSH.com, a loan information provider. "But that is starting to look less likely, given the still-soft state of the economy. Odds favor that the programs will continue until much later in the year, so mortgage rates should continue to be available at fantastic rates."
Low rates help existing homeowners even if they don't refinance their homes. Affordable loans boost homebuyer demand, sending home prices higher. They've recorded a 9% gain over the past 12 months, according to the S&P/Case-Shiller home price index.
The added home values mean some homeowners will no longer be underwater on their mortgages and can cash in the extra equity should they run into a rough financial patch. They can also sell their homes without resorting to a short sale, in which the price paid is less than what they owe on their mortgages. That saves sellers from a big hit on their credit scores.
If homeowners do refinance, they often choose 15-year, fixed loans. They are popular with borrowers seeking to shorten their loan terms -- saving themselves on total interest payments. The record low rates enable them to do that without increasing their monthly payments very much.
Borrowers with three-year-old, 30-year fixed-rate loans at 5% would have a monthly payment of about $537 for every $100,000 borrowed, and would pay out a total of about $93,000 in interest over the course of the mortgage. Switching to a 15-year at 2.57% would increase the payment only to $670 a month but the total interest paid out would come to less than $21,000.