File photo shows the headquarters of mortgage lender Freddie Mac in McLean
U.S. 30-year fixed-rate mortgages rose slightly to 3.90 percent in the week ending April 19, mortgage financier Freddie Mac said Thursday. REUTERS

U.S. 30-year fixed rate mortgage rates fell to 3.90 percent in the week ending March 1, down from 3.95 percent in the prior week, according to Freddie Mac.

The rate was down from 4.87 percent in the prior year.

Fixed mortgage rates bottomed out in January and February of this year, which is helping spur the housing market, Frank Nothaft, chief economist and vice president of Freddie Mac, said in a statement. For instance, pending existing home sales rose in January to its strongest pace since April 2010 and sales figures for December saw upward revisions.

The Federal Reserve also noted in its regional economic review Wednesday that residential real estate activity increased modestly in most areas during the early part of 2012, which included increased home sales.

The average 15-year fixed-rate mortgage rate was 3.17 percent, down from 3.19 percent in the previous week, and 4.15 percent in the previous year.

Five-year Treasury-indexed adjustable-rate mortgages (ARMs) averaged 2.83 percent, up from 2.80 percent in the previous week, but down from 3.72 percent in the previous year. One-year ARMs averaged 2.72 percent, down from 2.73 percent in the prior week and 3.23 in the previous year.