Home equity lines of credit (HELOCs) initially require borrowers to only pay interest, but that period will soon end for most borrowers. A government study shows that 58% of all HELOC balances will be required to start making principal and interest (P&I) payments between now and ’17. $15 billion in HELOCs will require P&I payments in ’13, rising to $53 billion in ’15 and to over $110 billion in ’18.