Average fixed mortgage rates in the U.S. fell in the latest week, with the 30-year-fixed rate reaching the lowest level in more than a year and a half, according to mortgage-finance company Freddie Mac (FMCC).

Freddie Mac Chief Economist Frank Nothaft noted Thursday that recent data indicated that new home sales missed expectations for October while the National Association of Realtors reported that pending home sales fell 1.1% in October. An employment survey compiled by payroll processor Automatic Data Processing Inc. and forecasting firm Moody's Analytics reported U.S. job growth for November also missed expectations.

For the week ended Thursday, the 30-year fixed-rate mortgage averaged 3.89%, the lowest level since the week of May 30, 2013. The 30-year-fixed rate was 3.97% a week earlier and 4.46% a year earlier.

Rates on 15-year fixed-rate mortgages averaged 3.1%, compared with 3.17% the previous week and 3.47% a year earlier.

Five-year Treasury-indexed hybrid adjustable-rate mortgages, or ARMs, on average, were at 2.94%, compared with 3.01% the previous week and 2.99% a year earlier. One-year Treasury-indexed ARM rates on average were 2.41%, from 2.44% the previous week and 2.59% a year earlier.

Write to Tess Stynes at tess.stynes@wsj.com

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