Westpac New Zealand's first half underlying profit rose 2 percent to $441 million, boosted by its digital banking business.
However, its bad debt was eight times more than the same time last year.
The Australian bank said its total first half net profit was $3.61 billion, $13 million less than it made in the same six-month period, a year earlier.
The bank said the Group's cash earnings were impacted by an $85 million tax charge, resulting from adjustments to derivatives and an increase in bad debt charges.
Total bad debt charges rose 2 percent, while in New Zealand, the bad debts charges were nearly 8 times more at $31 million, compared with $4 million, last year.
On the positive side, Australian customer deposits grew 2 percent, while New Zealand customer deposits grew 4 percent.