Mortgage rates retreated this week after the Federal Reserve’s decision not to raise its benchmark interest rate, according to data released Thursday by Freddie Mac.

Concerns about the worldwide economy, volatility in the U.S. stock market, and sluggish job and wage growth contributed to the Fed’s decision to hold off on a rate increase. Those same apprehensions had a dampening effect on mortgage rates. That’s good news for home buyers and homeowners looking to refinance.

The 30-year fixed-rate average sank to 3.86 percent with an average 0.7 point. (Points are fees paid to a lender equal to 1 percent of the loan amount.) It was 3.91 percent a week ago and 4.2 percent a year ago. The 30-year fixed rate has remained below 4 percent for more than two months.

The 15-year fixed-rate average dropped to 3.08 percent with an average 0.6 point. It was 3.11 percent a week ago and 3.36 percent a year ago.

Hybrid adjustable-rate mortgages also fell. The five-year ARM average slipped to 2.91 percent with an average 0.5 point. It was 3.92 percent a week ago and 3.08 percent a year ago.

The one-year ARM average slid to 2.53 percent with an average 0.2 point. It was 2.56 percent a week ago.

“Global growth concerns and lackluster inflation convinced the Fed to defer a hike in the Federal funds rate,” Sean Becketti, Freddie Mac chief economist, said in a statement.

“In response, Treasury yields fell about nine basis points [a basis point is 0.01 percentage point] over the week, with some larger day-to-day swings along the way.… Mortgage rates have remained below 4 percent for nine consecutive weeks and have remained range-bound between 3.8 and 4.1 percent since May. These low mortgage rates have supported strong home sales, and 2015 is on pace to have the highest home sales total since 2007.”

Meanwhile, as rates wandered down, mortgage applications soared this week, according to the latest data from the Mortgage Bankers Association.

The market composite index — a measure of total loan application volume – surged 13.9 percent from the previous week. The refinance index jumped 18 percent, while the purchase index rose 9 percent, its highest level in three months.

The refinance share of mortgage activity accounted for 58.4 percent of all applications.

“We saw significant rate volatility last week surrounding the [Federal Reserve] meeting, and rate declines toward the end of the week likely drove applications from both prospective home buyers and borrowers looking to refinance,” Mike Fratantoni, MBA’s chief economist, said in a statement.