Ulster Bank will start freezing current and deposit accounts on or after the 11th of November.
It will affect the first customers who received their six month notice in April this year.
Accounts will then be closed 30 days after they are frozen, for those the bank thinks, have a low reliance on the accounts or may have accounts elsewhere.
Meanwhile, the bank's confirmed the closure dates for the 25 branches, which then reopen as Permanent TSB branches.
They'll close on either the 6th or 13th of January.
Recently, research from the Competition and Consumer Protection Commission showed 60% of people who were switching banks from Ulster Bank and KBC which are both leaving the Irish market have had issues.
The survey earlier this month found one in eight customers haven't yet decided on a new bank.
That compared to one in four who hadn't decided in July.
