The number people on fixed-term mortgages has reached the highest level in more than two years.
Data from the Reserve Bank shows there were 543,100 fixed term home loans in May, more than in any other month since April 2011.
ASB chief economist Nick Tuffley says the increase has escalated in the past few months, as rate cuts are less likely and there is talk interest rates could be going up.
Mr Tuffley said mortgages with an interest rate fixed for one or two years have led the increase.
The Reserve Bank's figures show floating mortgages remain the most popular, with about 880,000 on the books in May.
However, on a monthly basis, figures show floating loans have been on a downward trend for more than a year.