WASHINGTON – The average U.S. rate for the 30-year fixed mortgage fell to a record low for a fourth straight week. Cheap mortgages have helped boost home sales modestly this year.

Mortgage buyer Freddie Mac said Thursday that the rate on the 30-year loan dipped to 3.78 percent. That’s down from 3.79 percent last week and the lowest since long-term mortgages began in the 1950s.

The average rate on a 15-year fixed mortgage, a popular option for refinancing, held steady at 3.04, matching the record low hit last week.

The average rate on the 30-year loan has been below 4 percent since early December. Lower rates are a key reason the housing industry is flashing signs of a recovery five years after the bubble burst.