That's because the Federal Reserve is keeping interest rates extremely low, a move that it hopes will boost the economy by encouraging individuals and businesses to borrow money and spend. Mortgage rates continue to creep lower. The average interest rate for a 30-year fixed mortgage in December, the close of the fourth quarter, was 3.35 percent, according to Freddie Mac. In September, the close of the third quarter, it was 3.47 percent.It's difficult to predict how long the low interest rates will last, which makes it difficult to predict how long refinancing can power mortgage results. "Could it last a couple more quarters? Sure, it could," chief financial officer Tim Sloan said in a call with analysts. "Could it last through the end of the year? Your guess is as good as mine, but there is a lot of opportunity out there." Wells Fargo's dominance in mortgages has helped it emerge from the financial crisis with a reputation as one of the strongest banks in the country. But the strategy also makes Wells Fargo a target for lawmakers, regulators and customers who blame risky mortgage lending for the 2008 global financial crisis. The latest example came Monday, when Wells Fargo and nine other banks agreed to spend a combined $8.5 billion to settle the government's charges that they had wrongfully foreclosed on some homeowners. Wells Fargo said it would pay $766 million and set aside an extra $1.2 billion for "foreclosure prevention actions," such as modifying mortgages for struggling homeowners. No one knows what other regulatory fines could be waiting for the banking industry. For some analysts, that makes the industry's future earnings a wild card. When Jefferies analyst Ken Usdin asked on a conference call how much more the bank might have to spend on buying back soured mortgages from investors, CFO Sloan replied: "The biggest mistake anybody in this industry can make is predict when that is going to end."