The Social Services Select Committee held back the changes giving IRD time to adjust its systems in order to implement the new formula.
Mr Dunne said the bill had been a long journey.
He said the changes would bring child support up to date and fairer for the 210,000 children and families involved in the scheme.
"We still have a long way to go, but as this bills stands we are a step close to having a more equitable outcome for children."
He said child support was a backstop when separated parents couldn't work out payments between them.
He said the current formula was too complex.
Labour's revenue spokesman David Cunliffe said the bill was a huge missed opportunity.
It should have been written into the bill that the interests of the child should always come first, he said.
Mr Cunliffe said the new formula was still not flexible enough to deal with the full range of family circumstances.