ASB Bank's first-half net profit rose nearly 7 percent but growth slowed toward the end of the year.
The bank's net profit of $444 million for the six months to the end of December came after more than 10 percent growth in net interest income, which offset increased provisions for bad debts.
ASB's December quarter profit growth slowed to just over 4 percent in the second quarter after more than 9 percent growth in the previous quarter.
The bank said the results reflected strong underlying growth across the bank's operating divisions.
Chief executive Barbara Chapman said the environment is very competitive, particularly in the home loan market.
ASB's sister company, insurer Sovereign, lifted its cash net profit by 43 percent to $57 million, with insurance income growing 22 percent.
The two companies' parent company, the Commonwealth Bank of Australia, reported an 8 percent rise in first-half net profit to $A4.5 billion.