WASHINGTON (AP) — Long-term U.S. mortgage rates rose this week but remain lower than they were a year ago.

Mortgage giant Freddie Mac said Thursday that the rate on 30-year fixed-rate mortgages rose to 3.94 percent, up from 3.93 percent last week. They stood at 4.30 percent a year ago. The rate on 15-year fixed-rate mortgages, popular among homeowners who are refinancing, rose to an average 3.38 percent, highest since March and up from 3.36 percent last week. But it still down from 3.52 percent a year ago.

The Freddie Mac survey was taken before Congress passed a sweeping tax-cut bill, sending other long-term rates higher.

"If those rate increases stick, we'll likely see higher mortgage rates in next week's survey," said Len Kiefer, Freddie Mac's deputy chief economist.

The rate on five-year adjustable-rate mortgages rose to 3.39 percent from 3.36 percent last week and 3.32 percent 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 unchanged at 0.5 point. The fee on 15-year home loans also remained at 0.5 point. The fee on an adjustable five-year mortgage was unchanged at 0.3 point.