WASHINGTON (AP) — Long-term U.S. mortgage rates edged lower this week.

Mortgage buyer Freddie Mac said Thursday the rate on 30-year, fixed-rate mortgages slipped to 3.89 percent from 3.90 percent last week. While historically low, that's still above last year's average of 3.65 percent. The benchmark rate stood at 3.43 percent a year ago.

The rate on 15-year, fixed-rate home loans, popular with homeowners who are refinancing their mortgages, fell to 3.16 percent from 3.18 percent last week.

Record-low interest rates have helped spur home purchases and boosted the housing market. Yet despite the low mortgage rates to lure prospective homebuyers, the housing market has remained hampered by tight mortgage credit, rising home prices and tight supply of homes on the market.

In the latest indication of low inventory constraining home purchases, real estate brokerage Redfin reported Thursday that sales in July declined 3.5 percent from a year earlier. The number of homes for sale fell 11 percent, marking 22 straight months of year-over-year declines in inventory, according to Redfin. There was a three-month supply of homes in July, higher than June's record-low 2.5 months but well below the six months that represents a market balanced between buyers and sellers.

To calculate average mortgage rates, Freddie Mac surveys lenders across the country between Monday and Wednesday each week. The average doesn't include extra fees, known as points, which most borrowers must pay to get the lowest rates. One point equals 1 percent of the loan amount.

The average fee for a 30-year mortgage was 0.4 point, down from 0.5 point last week. The fee on 15-year loans was unchanged at 0.5 point.

Rates on adjustable five-year loans rose to 3.16 percent from 3.14 percent last week. The fee declined to 0.4 point from 0.5 point.