Just over one-third of mortgage borrowers (35%) aren't completely sure of the interest rate they are paying, according to a new Bankrate.com report. That includes an alarming one in seven mortgage holders who are "not too confident," "not at all confident" or simply have no idea.

"Your mortgage rate is one of the most important numbers in your financial life, and there's a good chance that one of your neighbors has no idea regarding how much he or she is paying," said Holden Lewis, a senior mortgage analyst at Bankrate.com. "Given how far mortgage rates have fallen, these people could be missing substantial opportunities to save money by refinancing."

Mortgage rates are well below historical norms. The average fixed-rate 30-year mortgage is now 3.80%. It was well above six percent as recently as 2008, and in 2000, it was close to eight percent. 

Refinancing a $200,000 loan from 6% to 3.80% would save $267 per month; refinancing from 8% to 3.80% would save $536 per month.

Analysts expect mortgage rates to rise in the coming months. If rates hit 5%, one in five Americans say renting a home would become a better investment than buying.

The survey was conducted by Princeton Survey Research Associates International (PSRAI) and can be seen in its entirety here:

http://www.bankrate.com/finance/consumer-index/money-pulse-0215.aspx