The average long-term U.S. mortgage rate fell this week to its lowest level since mid-May, easing borrowing costs for prospective homebuyers.

The benchmark 30-year fixed rate mortgage rate fell to 6.43% from 6.49% last week, mortgage buyer Freddie Mac said Thursday. One year ago, the average rate was 6.67%.

Despite the modest decline from last week, the average rate is now at its lowest level since May 14, when it was 6.36%.

Borrowing costs on 15-year fixed-rate mortgages, often sought by borrowers refinancing a home loan, also declined this week. That average rate fell to 5.79% from 5.84% last week. A year ago, it was at 5.8%, Freddie Mac said.

Mortgage rates are influenced by several factors, from the Federal Reserve’s interest rate policy decisions to bond market investors’ expectations for the economy and inflation. They generally follow the trajectory of the 10-year Treasury yield, which lenders use as a guide to pricing home loans.