During the draw years the payment is interest only: the drawn balance times the annual rate divided by 12. During the repayment years the same balance is amortized with the standard monthly payment over the repayment term you enter. Total interest adds the interest-only months to the interest inside the repayment payments.
A $50,000 draw at 8% costs $333.33 a month in interest only. If that balance is then amortized over 15 years at the same rate, the repayment payment is higher because it includes principal. The form shows both payments.
A home-equity line’s real rate, draw rules, and minimum payment come from the lender. This page does not look up a bank’s prime rate or decide how much equity you can borrow.