Rates on all U.S. mortgages dropped in the latest week, with the 30-year fixed rate mortgage posting an all-time record low, according to mortgage company Freddie Mac Thursday.

“Interest rates for 30-year fixed-rate mortgage rates fell for the seventh consecutive week, moving these rates to the lowest since the survey began in April 1971,” said Frank Nothaft, Freddie Mac vice president and chief economist.

The average rate on the 30-year fixed rate loan plummeted more than a ¼ of a point to 5.19 percent, excluding fees, during the week ended December 18, down from 5.47 percent the previous week. One year ago, the average rate was 6.14 percent.

Rates on 15-year fixed rate mortgages also fell to a record low of 4.92 percent from 5.20 percent the preceding week. The 15-year mortgage rate has not averaged so low since the week of April 1, 2004. Last year at this time, the average was 5.79 percent.

One-year Treasury-indexed adjustable rate mortgages (ARMs) carried an average rate of 4.94 percent, down from 5.09 percent the week before. One year earlier, the average commitment rate was 5.51 percent.

Freddie Mac attributed the dramatic decreases to a historic move Tuesday by the Federal Reserve. “The decline was supported by the Federal Reserve announcement on December 16th, when it cut the federal funds target to a record low and stated it stood ready to expand its purchases of mortgage-related assets as conditions warrant,” Nothaft said.

The Fed promised to “employ all available tools” to get the economy back on a path of sustainable growth, suggesting that in the meantime “weak economic conditions are likely to warrant exceptionally low levels of the federal funds rate for some time,” the Fed said in a statement. The result would likely mean consistently low mortgage interest rates as well.