You get the rate in effect on the day you draw, applied only to what you draw. Nothing locks at approval. A HELOC (home equity line of credit) is a revolving line: you can be approved today and borrow months or years later, and because the lender has no way of knowing where rates will be when you tap the line, it is a variable-rate product. Mechanically, the rate is usually the prime rate plus a margin the lender sets based on your file. When prime moves, your HELOC rate moves with it. Most HELOCs adjust monthly with no cap on any single monthly change, though they carry a lifetime ceiling, commonly 18%. Terms vary by lender, so confirm the index, margin, and caps on any specific offer. With numbers: say you are approved for a $200,000 line today and draw $50,000 a year from now. You pay prime plus your margin as it stands on that draw date, on the $50,000 you actually borrowed. The untouched $150,000 costs you nothing in interest, and the rate that existed at approval is irrelevant. One feature worth asking about: some lenders, though far from all, let you convert an outstanding balance, in whole or in part, to a fixed rate at the fixed pricing available on the day you convert. If you expect to carry a chunk of the balance for a while, that conversion can pin it down.