WASHINGTON — The costs of borrowing to buy a home increased slightly this week, but U.S. mortgage rates are still near relative lows.

Mortgage buyer Freddie Mac said Thursday that the average rate on 30-year, fixed-rate mortgages rose to 3.94 percent from 3.88 percent last week. At this time last year, the benchmark rate was 3.47 percent. The historic average was roughly 6 percent.

Long-term home loan rates tend to track the yield on 10-year U.S. Treasury notes. The interest charged on 10-year Treasury notes has risen since early September, possibly in anticipation of tax cuts pushed by President Donald Trump that could cause the amount of government debt to climb.

Average mortgage rates began to rise after Trump’s election nearly a year ago in anticipation of tax cuts, climbing to as high as 4.32 percent at the end of last year. But rates began to slope downward again this year as the intended tax overhaul is unfolding at a slower and less certain pace than what the president promised.

The lower borrowing costs have helped preserve some affordability for would-be homebuyers, who are finding that home prices are severely outpacing incomes.

The average rate on 15-year, fixed-rate mortgages, popular with homeowners who are refinancing, rose to 3.25 percent from 3.19 percent last week. A year ago, the 15-year rate was 2.78 percent.

The average rate on the five-year, adjustable-rate mortgage increased to 3.21 percent from 3.17 percent last week.