The latest media reports have suggested that ASB is scrapping its floating home mortgage rate by 0.65 percent to 5.75 percent, along with increasing many of its fixed mortgage rates.
This has come as the bank's lowest floating rate in more than 40 years.
The fixation of the bank's rates appears ahead of the Reserve Bank of New Zealand's monetary policy statement next week.
ASB economists, who forecast this week that the central bank would slash its official cash rate by 25 basis points, admitted that market pricing implied only a 10 percent chance of it happening.
It is being predicted by a majority of economists that the official cash rate would remain unchanged at 2.5 percent.
A sum of $75 a month less will be paid by a customer with a $200,000, 20-year floating rate mortgage.
"ASB has also cut 0.3 percent from its business and rural base rates, bringing the business base rate down to 10.55 percent and the rural base rate to 7.6 percent. These new interest rates come into effect as from tomorrow for new loans, and on September 28 for existing floating and base rate loans," said a source.