WASHINGTON >> U.S. long-term mortgage rates rose slightly this week to their highest point in 12 weeks, though they remain far below their levels of a year ago.

Mortgage giant Freddie Mac said today that the average rate for a 30-year fixed mortgage rose to 3.75% from 3.69%the previous week. That’s down from 4.9% at the same time last year and by historic standards is very low.

Lower rates have helped reinvigorate the housing market, which stumbled last year. Sales of existing homes reached a 17-month high in August, though they fell modestly in September. New home sales jumped 15.5% in September from a year earlier. Single-family home construction has also ticked up.

The average rate on a 15-year mortgage moved up to 3.18% from 3.15% a week ago.

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 0.5 point, while the average fee for the 15-year mortgage was also 0.5 point.

The average rate for five-year adjustable-rate mortgages rose to 3.4% from 3.15% last week, while the feed was 0.3 point.