WASHINGTON (AP) — U.S. long-term mortgage rates fell for the fifth consecutive week, tipping the key 30-year loan average below 4% for the first time in nearly a year and a half.

The declining rates have been a boon to potential purchasers in the spring home buying season. Mortgage buyer Freddie Mac said Thursday that the average rate on the 30-year, fixed-rate mortgage fell to 3.99% from 4.06% last week. It was the first time it ran below 4% since January 2018. By contrast, a year ago the benchmark rate stood at 4.56%.

The average rate for 15-year, fixed-rate home loans declined this week to 3.46% from 3.51%.

The escalating trade war between the U.S. and China continued to pound stock prices this week in a continued volatile market. The U.S. stock market was on track Thursday afternoon for its fourth straight weekly loss and its first monthly decline of the year.

Nervous investors continue to shift money from volatile stocks to the bond market, pushing up bond prices and depressing their yields. The yield on the 10-year Treasury note, which influences mortgage rates, was 2.26% late Wednesday, its lowest level in nearly two years. It fell further to 2.24% at midday Thursday.

Freddie Mac surveys lenders across the country between Monday and Wednesday each week to compile its mortgage rate figures.

The average doesn't include extra fees, known as points, which most borrowers must pay to get the lowest rates.

The average fee on 30-year fixed-rate mortgages was unchanged this week at 0.5 point.

The average fee for the 15-year mortgage rose to 0.5 point from 0.4 point.

The average rate for five-year adjustable-rate mortgages fell to 3.60% from 3.68% last week. The fee remained at 0.4 point.