Social Development Minister Paula Bennett says projected savings of $1 billion from the proposed welfare changes is a "best guess".
The first phase of the changes is expected to cost $287 million over four years.
It includes $148 million to be spent on budgeting and parenting courses, with youth beneficiaries, aged 16 to 17, getting incentives of up to $30 per week for taking the courses.
It also provides up to $64 million going to private providers of youth services.
Ms Bennett says the entire welfare package is expected to cost at least $520 million and save $1 billion over four years.