Video - The National Party leader says there are still outstanding issues and further talks are needed before a government can be formed.
Formal coalition talks with National and Labour wrapped up on Thursday, and New Zealand First MPs met on Friday to go through the proposed deals in detail.
The party's leader, Winston Peters, has not been able to say how long the board will take to make a decision.
The National Party could govern with New Zealand First alone, but Labour has to bring in both New Zealand First and the Greens to form a government.
Watch National Party leader Bill English on Morning Report here:
Mr English told Morning Report there were still unresolved issues and further talks were needed.
The two parties had been in contact over the weekend to clarify stances on various policies, he said.
"While New Zealand First are having a discussion today they won't be dealing with completed agreements because there's still outstanding issues."
Things that remained on the table included ministerial portfolios, as the only things discussed so far were policy matters.
"We come to this negotiation with 56 seats in the Parliament, significantly the largest party.
"That's reflected in the weight of discussion about the policies so far, but there are still matters that need to be completed."
He expected an announcement by the end of the week but was not "putting deadlines on it".
"We certainly want to get on and get the process completed, I think the public are expecting the formation of a government pretty shortly."
Mr Peters' self-imposed deadline of last Thursday was "a bit optimistic".
"[Especially] if you're going to have intensive policy discussions with the National Party on one hand, and Labour and the Greens and a more complicated discussion on the other hand, and expect to get it all done in a few days."