That included a Covid-19 impairment of $108m and a software capitalisation policy change that reduced BNZ's capitalised software balance.
Excluding those items, statutory net profit decreased by $74m, or just 13.5 per cent, compared to 2019.
BNZ had cash earnings of $562m for the half - up 5.6 per cent compared with $532m in the previous first half.
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"We went into the crisis with a well capitalised balance sheet and funding and liquidity," Mentis said.
"We've done top ups for our credit reserves to ensure that we're well positioned for the tougher economic conditions ahead."
The BNZ was working off a base assumption that we will see the economy contract by 9 per cent in 2020, unemployment will rise to 10 per cent and house prices drop by 10 per cent.
But there was a range of possible scenarios, Mentis said.
For some sectors and businesses, the path to recovery is going to be very challenging, she said.
"The response from the Government, Reserve Bank and the banks has been very decisive," she said.
"We've all moved at pace. That is going to help cushion and help many more customers get through this than might otherwise have been the case."
BNZ had been working closely with large numbers of business customers to get a picture of the economic impact.
It has also been crunching data on cash flows using credit card and debit card statistics.
To date the BNZ had provided assistance for more than 17,000 business customers to a value of $16 billion - using a mix of its own support measures and the government-guaranteed loan scheme.
It also had 21,000 home loan customers seeking to adjust the structure of their mortgages.
About 55 per cent of those were opting for interest only, about 19 per cent had opted for lower repayments with 26 per cent taking up the six-month payment deferral.
In total more than 230,000 customers had been in contact to discuss their banking situation at some level, Mentis said.
She said she didn't expect the level of impaired loans to rise dramatically in the next six months because there would still be high levels of government support.
"As they come off that's when you're going to see more of the stress," she said.
Bank data was highlighting the stress points in the economy with credit card and debit card use offering insight into cashflow by sector and region.
Unsurprisingly the biggest falls had been in areas like travel, hotels and restaurants - down 98 per cent, 70 per cent and 65 per cent respectively.
But some had gone the other way, Mentis said.
The IT and software sector and seen a 60 per cent rise in positive cashflow and the food category a 47 per cent rise.
The data showed the biggest stress is happening around micro and small business, Mentis said.
Sectors like accommodation, cafes and restaurants were most stressed in the past three weeks with outgoing costs twice as large as incoming revenue.
More than 28,000 BNZ business customers had taken government wage subsidies, predominantly cafes, accommodation and restaurants, she said.
Smaller regions also appeared to be disproportionately impacted.
Dunedin, the Western Bay of Plenty and Hamilton, Stratford and the Grey District were all seeing micro-businesses experience declines in cashflow faster than average.
"I've talked to many business owners across the country and they all want transparent conversations about their business so they can make sound decisions," Mentis said.
"We know that for some sectors the path to recovery is going to be very difficult. And difficult enough without further increasing their debt levels … so really important that we all work together."
She was broadly optimistic though.
"Businesses can't wait to get back to work," she said.
"Every business customer I've spoken to is really using this as an opportunity to think about their business, to change the way they're operating, to think about digital and to think about their fixed costs."
• Covid19.govt.nz: The Government's official Covid-19 advisory website