Mortgage rates hit an all-time low this week, according to new data from Freddie Mac.

The 30-year fixed-rate mortgage averaged 2.86% this week, according to Freddie’s Primary Mortgage Market Survey. That’s the lowest rate in the history of the survey, which dates back to 1971.

“Mortgage rates have hit another record low due to a late summer slowdown in the economic recovery,” said Sam Khater, Freddie Mac’s chief economist. “These low rates have ignited robust purchase demand activity, which is up 25% from a year ago and has been growing at double-digit rates for four consecutive months. However, heading into the fall it will be difficult to sustain the growth momentum in purchases because the lack of supply is already exhibiting a constraint on sales activity.”

The 15-year FRM also dropped this week, down to 2.37% from last week’s 2.42%. A year ago at this time, the 15-year FRM averaged 3.09%.

The 5-year Treasury-indexed adjustable-rate mortgage averaged 3.11% this week, up from last week’s 2.93%. last year at this time, the 5-year ARM averaged 3.36%.