HELOC payments are based on the interest which is set by the lender, the interest is calculated on the amount that you borrow only (For example $100,000 line, the amount used is $10,000, the interest charge is on $10,000 only). Any additional amount on top of your minimum will pay off a part of the principal, those funds go back to your line amount. When the draw period reaches maturity, you enter a repayment period, where you begin paying back the remaining principal on your HELOC, plus calculated interest.