Fixed-term tenancy agreements entered into from 11 February 2021 automatically convert to periodic tenancy agreements unless:

• the landlord gives notice using the reasons listed in the Residential Tenancies Act for terminating a periodic tenancy, or
• the tenant gives notice (for any reason) at least 28 days before the end of the tenancy, or
• both landlord and tenant agree to extend, renew, or end the fixed-term tenancy before it expires.

Section 50 of the Residential Tenancies Act 1986 has more information(external link) — New Zealand Legislation website