Kiwi Group, which owns KiwiBank, has more than doubled its annual profit.
The group's net profit was $122 million for the year to June, up from $58m the year before. This included a large write-down on the upgrade of its IT systems.
The profit arises partly from improvements in interest margins and a low level of bad debts.
The underlying profit, which excluded the year's earlier costs, was up 3 percent to $133m.
The bank's interest income rose nearly 5.8 percent to $879m, with net interest income of $411m, reflecting a lower cost of borrowing.
Cutomer deposits rose 1.2 percent, while lending rose 2.7 percent.
"The real story is that KiwiBank has significantly reduced fees for personal customers," chief executive Steve Jurkovich said.
"This has been done through either dropping or removing fees altogether."
KiwiBank was the biggest income generator for the group and contributed $115m to the bottom line profit.
The other parts of the group - Kiwi Wealth, New Zealand Home Loans and Kiwi Insure - had all grown their businesses.
Overall, Mr Jurkovich said profitability and rates of return provided momentum into the current financial year.