Britain's over-50s are currently £2.7 billion overdrawn, data from uSwitch.com reveals.
Almost 12 million over-50s currently have an overdraft on their bank account, the independent comparison service calculates, with 4.5 million people regularly going into the red.
Additionally, 1.5 million over-50s regularly rely on their overdraft to pay bills, 1.2 million use their overdraft to pay for the weekly shopping, and 850,000 are permanently overdrawn.
The average overdraft balance among over-50s is £615, with one in eight more than £1,000 overdrawn.
"These figures shatter the myth that 'debt' is something that only affects the younger generations in this country," said Nick White, uSwitch head of personal finance.
"At a time when the only interest rates the nation's elderly should be worrying about are those on their savings accounts, too many are finding out how expensive it is to borrow on an overdraft - or worse still, to go overdrawn without authorisation."
In total, the nation's over-50s pay some £330 million a year in interest on their overdrafts, with 28 per cent of people going over their agreed overdraft limits - incurring extra charges and higher interest rates than normal.
"As the banks cash in on over £568 million in interest and penalty charges, the over-50s are left to worry about their retirement and the financial shortfalls that they are faced with in the immediate future," said uSwitch's Mr White.
"It seems that the banks are not concerned that they are lending money to customers who are close to, or have already reached, retirement age. Quite the opposite, in fact, with one in five of those surveyed over the age of 50 saying that that their bank had increased their overdraft limit without being asked to do so."