You’ll almost always encounter variable interest rates with HELOCs, The variable interest rates on HELOCs are partly determined by benchmark indexes, like the U.S. prime rate. The prime rate is set by individual banks and influenced by fluctuations in the federal funds rate (the rate that banks charge other banks for short-term loans). For HELOCs, lenders typically take the benchmark’s interest rate and add several percentage points to it to come up with your credit line’s interest rate.Some lenders offer fixed-rate HELOCs, which allow you to lock in a portion of your HELOC balance with a set, unchanging interest rate. This essentially converts part of your HELOC into a home equity loan. With a fixed rate, you won’t need to worry about your interest rate increasing over time.