Kiwibank says its 4.99% one-year fixed mortgage rate is the biggest thing the bank has ever done.
It announced today that the offer will expire at the close of business tomorrow.
It has been available for just over a month.
The rate was only available to those with 30% equity in their property but bank spokesman Bruce Thompson said it had generated hundreds of millions of dollars of business.
He described the response to the offer as stunning.
Half of those taking up the rate were customers new to the bank.
"I think people are looking for some level of certainty. You have some commentators saying the rates are going to fall and some saying they are going to go up. This gives certainty for a year at a very low rate - possibly the lowest in 40 years. It's almost a post-war rate."
He said people who had submitted an application would receive the rate, even if the loan had not been set up by the time the offer expired.
