Four fifths of credit is due to expire before this summer, said the airline.
"Given New Zealand's border has only fully reopened in the last couple of months, we think it's the right thing to do to extend the expiry of credits given customers haven't had many opportunities to use them," said the airline's head of Customer Leanne Geraghty.
The airline hopes new routes, including the flagship Auckland - New York direct service which launches this weekend, will entice passengers to use credit held with the airline.
Another factor keeping passengers from using credit is the prohibitively high cost of air travel at the moment.
Lack of capacity and the soaring cost of jet fuel have seen international and domestic air fares skyrocket.
On Wednesday, Air NZ chief executive Greg Foran told the Herald that on average domestic fares are up 20 per cent over a three week period.
The return of more seats and more rival airlines will hopefully put some downwards pressure on fares.
Australian carrier Qantas recently announced it would be going head to head with Air New Zealand, launching its own Auckland to New York service from June, next year.
Any new credits issued from 1 October 2022 will have a 12-month expiry date to book new flights and a further 12 months to travel.