Locking in a fixed rate on a portion of their credit line can make sense for some borrowers, says Greg McBride, senior financial analyst with Bankrate.com. "You can mitigate the risk of rising rates in the short-term while still preserving your ability to tap into the line of credit as needed," he says.

Terms and costs for locks vary. At National City, for instance, borrowers who lock in a portion of their credit line can elect to make interest-only payments on the locked-in portion for the first seven years or pay interest and principal on that amount over five, 10, 15 or 20 years. National City charges $50 each time a borrower wants to fix the rate on some or all of their credit line, while SunTrust Banks Inc. levies a $15 fee. At Bank of America, borrowers can take up to three locks at no charge.

Corrections & Amplifications:

At Wells Fargo, the rate at which borrowers are prepaying their home-equity lines of credit is 36% higher this year than last year. This article incorrectly put the increase at 50%.