A number of companies which hedge term debt, particularly infrastructure companies - such as Mighty River Power, Contact Energy and Transpower - with 30 June balance dates are likely to be reporting windfall profits.
Bancorp Treasury Services senior client advisor Peter Cavanaugh said such companies with long-term debt are required by accounting rules to mark their hedge contracts to market.
"Large borrowing organisations, most prominently your infrastructural companies in New Zealand, they use such products as interest rate swaps which at their balance date have to be valued in relation to the market at the time."
Mr Cavanaugh said last year because interest rates swaps were in place and interest rates had fallen, quite substantial losses on that drop were recorded.
He said there has been the opposite effect in the last 12 months.
Mr Cavanaugh said if interest rates remain where they are today by the end of the month, then there would have been a more than 0.75% increase in the five-year swap rate and a 0.85% increase in the 10-year swap rate.
He said allowing for any cash flow over the past year, it means that anything that was reset at interest rates that applied on 30 June 2012 will now be revalued at much higher interest rates.
Mr Cavanaugh said borrowers will benefit from having interest rates in place at a lower than prevailing market rate and it will affect the company's profit-loss statement.
He said it will be a non-cash item but that in some cases the revaluation could be quite substantial.