Election day is here, but for millions of Australians, casting their vote is now a thing of the past.

More than 4.7 million votes were cast ahead of today, thumping previous records for early voting.

It's undoubtedly going to have an impact on when we'll know the outcome from the more than 16 million votes Australians will cast in the election.

Here's what we know about when an outcome is likely.

Have they started counting all these early votes?

Historically, first preference results for some small districts are usually finalised from about 8:00pm, with the bulk of the remaining districts finalised after 9:00pm.

Then, election officials in each polling booth will determine the two-candidate preferred count. It's this count that determines who wins the seat.

The earliest results that will come in are likely to be from small polling places, which tend to be in regional seats, meaning the Liberal and National parties should fare well in early results.

Expect Labor to do better when the bigger metropolitan polling booths start reporting results.

Seats with the smallest numbers of candidates are also likely to come in sooner than electorates with big fields.

How long will it take to count the votes?

Historically, first preference results for some small districts are usually finalised from about 8:00pm, with the bulk of the remaining districts finalised after 9:00pm.

Then, election officials in each polling booth will determine the two-candidate preferred count. It's this count that determines who wins the seat.

The earliest results that will come in are likely to be from small polling places, which tend to be in regional seats, meaning the Liberal and National parties should fare well in early results.

Expect Labor to do better when the bigger metropolitan polling booths start reporting results.

Seats with the smallest numbers of candidates are also likely to come in sooner than electorates with big fields.

When will Antony Green call the election?

Just a reminder, the ABC's chief elections analyst doesn't determine the outcome.

Antony Green uses statistics to make a prediction of the outcome, but that could happen later than other years.

In 2013, Green was confident by 6:45pm that Labor would lose based on the early figures, but in 2007, when the Coalition lost, he had to wait until after 7:00pm because of time zone differences on the east coast.

The election commissioner has warned there could be delays in knowing the results on the night thanks to the record levels of early voting.

Green told ABC News Breakfast this week that a close result would further delay calling the election.

But he remains optimistic he will be able to call the election if it's in line with recent opinion poll trends.

The exact time of that will depend on how long it takes for the electoral commission to release the results.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 57 seconds 57 s Gigantic pre-poll centres could cause headaches, says Antony Green

What about the Senate?

Unlike the 2016 double-dissolution election, only half of the senators are facing re-election.

Senators not facing election: Coalition: 16

Coalition: 16 Labor: 13

Labor: 13 Greens: 3

Greens: 3 Centre Alliance: 2

Centre Alliance: 2 One Nation: 1

One Nation: 1 Australian Conservatives: 1

There are 76 seats in the Senate and 34 votes are needed to control the chamber.

The Coalition starts ahead of Labor, with three extra seats.

The outcome of the Senate vote could have a major implication on the next federal government, with the neither the Coalition or Labor expected to have outright control.

Once polling booths have counted the Lower House votes, election officials will then start counting the Upper House ballots.

These ballots will be sorted into first preferences for above-the-line and below-the-line voting.

Six senators from each of the states, and two from each of the territories, will be elected this year.

Election observers expect four to five winners from each state will be known on the night, with the sixth position likely to take weeks to finalise.

When will we know the official final outcome?

After polling day, votes will be rechecked to ensure the accuracy of the first count.

Once all the votes are counted and checked, the AEC will then declare the final results in each electorate.

The writs (a technical term for the legislation that governs an election) must be returned by Friday, June 28 at the latest.

The Parliament must then sit within 30 days of the writs being returned.