WASHINGTON (AP) — The average 30-year U.S. mortgage rate remained at a 52-week low of 4.10 this week.

Mortgage company Freddie Mac also said Thursday that the average for a 15-year mortgage, a popular choice for people who are refinancing, rose to 3.25 percent from 3.23 percent.

At its 52-week low of 4.10 percent, the rate on a 30-year mortgage is down from 4.53 percent at the start of the year. Rates have fallen even though the Federal Reserve has been trimming its monthly bond purchases, which are intended to keep long-term borrowing rates low. The purchases are set to end in October.

The low rates appear to have boosted U.S. home sales. Data released Thursday showed that more Americans signed contracts to buy homes in July. The National Association of Realtors said its seasonally adjusted pending home sales index rose 3.3 percent to 105.9 last month. Still, the index remains 2.1 percent below its level a year ago.

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 0.5 point, unchanged from last week. The fee for a 15-year mortgage remained at 0.6 point.

The average rate on a five-year adjustable-rate mortgage rose to 2.97 percent from 2.95 percent. The fee stayed at 0.5 point.

For a one-year ARM, the average rate edged up to 2.39 percent from 2.38 percent. The fee was stable at 0.5 point.