Last month, the Commerce Commission announced 21 criminal charges against the bank, for errors resulting in more than 36,000 customers being overcharged by $7 million.
Kiwibank reported itself to the commission, apologised to customers and had started the process of refunds.
The charges related to overcharged fees and interest rates on home loans, credit cards and overdrafts since 2019.
The commission said there had been problems since Kiwibank was established in 2002.
Kiwibank chief executive Steve Jurkovich said the bank "proactively" identified the problems and "fully co-operated" with the commission's investigation.
"While I'm disappointed with the mistakes we made in the past, I'm proud of the way our team has now come together to fix the problems and make things right for our customers," Jurkovich said.
Kiwibank said the bank and the commission were "aligned in their views on the appropriate penalty", which would be determined by the Auckland District Court.
