BNZ customers could be getting an unexpected payment this week after the bank realised it made an error with some documentation.
It announced on Tuesday it will be refunding a total amount of $3.8 million to around 10,000 customers.
The bank said in a statement the mistakes were made when the Credit Contracts and Consumer Finance Act (CCCFA) was implemented in 2015.
The Act was designed to make interactions between borrowers and lenders clearer but BNZ missed some of the requirements in 2015.
It failed to send out some confirmation letters quickly enough when customers changed their account. It also missed information in some documentation and set up some accounts with old documentation.
BNZ CEO Angie Mentis said the bank is working to make things right.
"No customers were overcharged, but we didn't get it 100 percent right," she said.
"While mistakes do happen from time-to-time, finding those mistakes and fixing them is simply the right thing to do for our customers."
The average refund to consumers will be around $375, although the lowest amount owed is $0.01. Any refunds lower than $4.99 will be rounded up to $5.
A letter confirming the refunds will be sent to BNZ customers this week, and those with a BNZ account will have the money deposited in their account on Wednesday.
Anyone without an account will receive a cheque in the mail.