Mortgage rates shot up for the week ended Sept. 18, making their biggest one-week gain so far this year, the latest Freddie Mac Primary Mortgage Market Survey found.

This is the highest rates have been since the week ended May 1, 2014.

The 30-year, fixed rate mortgage averaged 4.23%, a jump from 4.12% last week, but still down from 4.5% a year ago this time.

The 15-year, FRM grew from 3.26% a week ago to 3.37%. Last year, the 15-year, FRM averaged 3.54%.

In addition, the 5-year Treasury-indexed hybrid adjustable rate-mortgage hit 3.06%, an increase from 2.99% last week. This is barely down from 3.11% last year.

The 1-year Treasury-indexed ARM was the only rate to decline, falling to 2.43% from 2.45%. In 2013, the 1-year ARM averaged 2.65%.

“Fixed-rate mortgage rates rose this week following the increase in 10-year Treasury yields being partially fueled by market speculation the Federal Reserve might change its interest rate guidance. Meanwhile, the Labor Department reported that its Consumer Price Index declined 0.2 percent in August reflecting declines in energy prices. Excluding food and energy, the CPI was unchanged,” said Frank Nothaft, vice president and chief economist with Freddie Mac.

Bankrate also noted that although mortgage rates were up very modestly this week, it is enough to put the benchmark 30-year fixed mortgage rate at a 3-month high.

The 30-year, FRM edged higher to 4.33%, compared to 4.27% last week.

The 15-year, FRM escalated to 3.46%, up from 3.42% a week prior, while the 5/1 ARM grew to 3.35%, up from 3.29% a week ago.