Tens of millions of voters will enter ballot boxes across the United States on Tuesday.

But election results — including whether Kamala Harris or Donald Trump will become the next president — won’t be official until the votes are counted and verified, and that process could take days to be fully completed.

States in the battlefield that are expected to determine the winner of the election, the process will be closely scrutinized. Trump already questions the reliability of many voting processes and challenged the results of many of the votes in court in 2020.

Here’s what you need to know about voting in 2024.

The first polls will begin closing at 6pm EST (23:00 BST) on Tuesday, but the counting of votes will take much longer than that time.

In many cases, it can take weeks to get an official number, due in part to state rules.

For example, in two battleground states—Pennsylvania and Wisconsin—election officials are not allowed to process mail-in ballots until election day. This is expected to significantly slow down the count.

It’s worth noting that news organizations use unofficial results and predictions when announcing winners on election night or in the days that follow, rather than waiting for final, official tallies.

Counting also varies from region to region and depends on the equipment used.

Some counties “feed” ballots into optical scanners, while others use touch-screen systems or ballot marking devices to record votes.

Browsers are the most common. They then tabulate the results, which are manually counted and double-checked by hand.

The results are shared with election officials, parties and finally with the public.

The counting process may be slowed by interruptions, legal challenges, or difficulties with provisional ballots.

Numerous legal challenges have already been filed.

As of Nov. 1, there were 203 voting and election lawsuits pending in 40 states, according to Marc Elias, the Democratic election lawyer who filed many of the responses to Trump’s lawsuits in 2020.

By his count, they are concentrated in Georgia’s battleground states of Pennsylvania, North Carolina, Wisconsin and Arizona, which faces 25 legal challenges.

Provisional ballots are given to voters for whom it is unclear whether they are eligible to vote. This can happen, for example, if a person cannot be found on the registered voter rolls.

Ballots may also be challenged by election workers or, in some states, poll watchers. When challenged, ballots must be reviewed by election auditors and submitted to state canvassers before being included or excluded from official final tallies.

Each state has its own procedure for recounts and what might trigger them.

In the battleground states of Pennsylvania and Michigan, recounts occur automatically when the number of votes each candidate receives is particularly close.

In the case of Pennsylvania, for example, an automatic recount is required if the margin of victory is equal to or less than half a percentage point.

Recounts can also be requested by candidates, courts, or groups of voters, although the rules vary significantly among states.

A request must usually be made within three to seven days.

For example, in the crucial state of Arizona, a recount must be requested within two days of unofficial results being announced.

Again, the results the public hears on election night are unofficial; instead it is a mix of preliminary data released by officials and estimates from the Associated Press news agency, or Reuters.

All states must certify their official results by December 11.

However, many important states have earlier deadlines. For example, Georgia must certify its final count by November 22, while Michigan and Pennsylvania have until November 25.

The next step will occur six days later, on December 17, when presidential “electors” meet and send their states’ results to Congress.

Electoral votes must be received by the Senate President – the Vice President, in this case Kamala Harris – by December 25th.

The state’s voters came under intense scrutiny in 2020, when Trump and officials in seven states tried to use alternative or “fake” voters to overturn his election loss.

This year, some expect the certification process to be dragged out by legal battles, including numerous potential challenges from Trump and his political allies in Pennsylvania.