The number of tightly contested seats has more than doubled compared with previous federal elections, pushing back formal results.
The Australian Electoral Commission says up to 75 electorates have to undergo full preference distribution for the election of a candidate.
Many seats will not be declared by the commission until next week, with a number to receive formal results as late as the June 28 deadline.
A "sizeable" increase in postal votes has also delayed verification and counting.
A record number of voters casting ballots for micro-parties or independents has "changed the nature of the count", with preferences taking longer to calculate.
Electoral Commissioner Tom Rogers says rigorous counting and verification processes ensure the integrity of the election.
"Right, not rushed - it's a key principle for us and despite an understandable external desire for things to be wrapped up quickly, it is a principle that maintains the strength of Australian elections," Mr Rogers said.
"We will deliver legal, transparent and trusted results by the legislated deadline."
The commission has completed 135 three-candidate-preferred counts in required electorates.
By the end of Tuesday, 14 out of 151 lower house seats will be been formally declared, with a number of other declarations slated for Wednesday and Thursday.
Counting for the Senate continues, with results expected in smaller states and territories by the middle of next week.