Profit margins at the big banks have hit their highest levels since before the global financial crisis, a report has found.
Relatively small losses on derivative products meant a slightly lower dollar profit for the big banks in the first half of the 2012 financial year.
But the five biggest banks - ANZ National, BNZ, Westpac, ASB and Kiwibank - still made a pre-tax profit of $2.4 dollars.
And the profit margin - the difference between what the banks paid in interest to borrow money and what they charged to customers - was its highest in six years.
Accounting firm PWC, which analysed the banks' results, says the record numbers with floating mortgages, which are cheaper for the banks to fund, is behind the increase in margins.
The banks says those margins are back under pressure and future profits will not be as high.
The Bankers Association says a shift back to fixed rates and increasing red tape following the global financial crisis means margins are coming down again.