The main difference between a testamentary guardian and a welfare guardian in Aotearoa New Zealand is that a testamentary guardian is appointed for a child, while a welfare guardian is appointed for an adult. 

Testamentary guardian

A parent names a testamentary guardian in their will to care for their child if they die. The guardian's role is to support the child's welfare and make important decisions, such as about their education and health. The guardian must be at least 20 years old and only one can be appointed. The guardianship ends when the child turns 18. 

Welfare guardian

A welfare guardian is appointed to make decisions about a person's care and welfare, such as where they live, their medical treatment, and their care arrangements. The guardian must be at least 20 years old, act in the person's best interests, and have no conflicts of interest. They must also provide written consent to their appointment. A medical assessment is required to determine if the applicant has the capacity to make decisions and communicate them.