This time last year the average one year fixed term mortgage rate was 6.04 per cent across the banks, according to Interest.co.nz.
The fall has prompted mortgage holders to break their fixed term agreements to shift to a better rate.
Banking Ombudsman Nicola Sladden said people were generally aware there was a cost to breaking their loan early to get a better deal.
"But they don't always accept how it is calculated."
Sladden said the banks used quite complex formulas for working out the costs and the formulas varied across the banks.
"It is not just retail interest rates that influence it."
Sladden said people should ask their bank to explain how the fee will be calculated before they sign any loan documents.
"I think people are aware there is a cost associated with it. The miscommunication is how the break cost is calculated and how it can change over a short period of time.
"The key is for banks to explain how the cost is made up so people can understand it."
The ombudsman scheme has produced a quick guide for people who are concerned about the costs associated with breaking their fixed term mortgage.