Economics can helpThe average 30-year fixed-rate mortgage hit 6.66% this week, according to the Federal Home Loan Mortgage Corp., commonly known as Freddie Mac. That's the highest it's reached in a year — at the end of last July, the average rate was 6.72%. It's considered an indicator of which way other interest rates are trending — and mortgage rates closely follow. "Oil prices always swing mortgage rates," said Kara Ng, senior economist at Zillow. Those same investors were also spooked after the Federal Reserve on Wednesday signaled that an interest rate hike could be on the way in September, even as it held its benchmark interest rate steady for now.