The country is unlikely to know who wins the battleground state of Pennsylvania on election night. That’s because of a quirk in Pennsylvania’s laws.

I am an assistant professor of political science at Gettysburg College in Gettysburg, Pennsylvania, where I teach and conduct research in American politics, public opinion, voting and elections. I have previously explained why Pennsylvania is crucial to both the Harris and Trump campaigns, and why Pennsylvania will likely prove pivotal in determining the presidency.

Here are five things that are important to understand about the timing of the election outcome in Pennsylvania.

The state sets the rules for voting and counting

Under the U.S. Constitution, states and the federal government share power. Some powers are exclusively reserved for the states, while other powers are exclusively under the control of the federal government, for instance signing treaties, or declaring war on a foreign nation. Under this system, known as federalism, states – not the federal government – run elections. Individual states and local jurisdictions within states determine polling locations, how citizens vote and other rules surrounding election administration.

Elections are run differently across states. Some states require photo identification at the polls when you vote, while some verify identities of voters in other ways.

Differences also extend to how ballots are counted and how long it takes for states to report results.

Nearly all states prohibit releasing election results until after the polls close on Election Day. However some states begin to count mail-in and early ballots as they are cast. This means that they can report the results of an election sooner on Election Day, because the work of processing and counting is already done.

Under Pennsylvania law, voters may cast ballots through the mail. Local election officials are prohibited from opening the envelopes containing mail-in ballots until 7 a.m. on Election Day.

Read more: Why Pennsylvania is the key to a Harris or Trump Electoral College victory

Prior to 2020, the only Pennsylvania voters permitted to vote by mail needed an excuse – for instance, serving overseas in the armed forces. The first time Pennsylvania voters were able to vote by mail without an excuse was in 2020. Due to the COVID-19 pandemic, a record number of voters nationwide chose to vote by mail when that option was allowed, including in Pennsylvania.

Out of the nearly 7 million total Pennsylvania voters in the 2020 presidential election, roughly 2.6 million voted by mail. Prior to 2020, local election officials never needed to count such a large number of ballots received through the mail, and news organizations could typically announce Pennsylvania’s unofficial winner quickly.

For instance, in 2016, media organizations could project a Trump victory in Pennsylvania at 2:29 a.m. the Wednesday after Election Day. But in 2020, it took four days for enough ballots to be counted for news organizations to project that Joe Biden won Pennsylvania and would be the next president.

As of 10 a.m. on Oct. 28, 2024, about 2.09 million Pennsylvania voters had requested mail-in ballots. That number was likely to increase, as Pennsylvanians could request a mail-in ballot until Oct. 29. County boards of elections must receive mail-in ballots by 8 p.m. on Election Day for those ballots to be counted. Members of the military and overseas absentee ballots have until Nov. 12.

Mail-in ballots take time to count

It’s impossible to definitively say how long it will take to know who won Pennsylvania. The more ballots there are to count, the longer America will need to wait.

The length of time it will take to determine the winner will also depend on how close the election turns out to be.

If the margin of victory for the winning candidate is very small – say tens of thousands of votes – then election officials will need to count enough ballots that it becomes mathematically impossible for the other candidate to catch up, regardless of how the remaining ballots voted and only then will credible news organizations announce a projected winner of each state.

If the election is within half a percentage point, Pennsylvania state law dictates that an automatic recount is required, although recounts are unlikely to change the winner of a statewide race.

But the wait may not be as long as it was in 2020

Although no one can say for certain how long it will take – anyone who says otherwise is wrong – there are indications that it might not take as long as it did in 2020.

First, it is highly likely that fewer Pennsylvanians will choose to vote by mail in 2024. A smaller proportion of voters opted to vote by mail in the 2022 midterm election than in the 2020 general election, and that trend is likely to continue in 2024. Thus far, fewer voters have requested mail-in ballots than in 2020, so that assertion is supported by the available data at this point.

Counting may also take less time because election officials have more experience counting the mail-in ballots now than in 2020. That year was the first time election officials counted so many mail-in ballots.

Counties have also secured better machines to assist in the process. For instance, Philadelphia County will use new machines to help them open the envelopes faster. This should speed up the process, according to Pennsylvania’s chief elections official, Secretary of State Al Schmidt, a Republican, although Schmidt recently told NPR news it is unlikely that a winner will be declared in Pennsylvania on election night.

One more thing to expect

According to the Associated Press, Pennsylvania will report small batches of mail-in ballots first, followed by in-person Election Day votes. After that, the remaining mail-in ballots will be tabulated and released. This process will likely result in predictable patterns in the results of the election.

We know several things because of who in Pennsylvania has requested mail-in ballots this cycle, which follows a similar pattern as in 2020. Most voters who opted to vote by mail in 2020 were Democrats, while Republicans were more likely to vote in person on Election Day.

The results for in-person, Election Day voters can generally be reported faster. That’s because voters themselves will feed their ballots into vote tabulating machines at various precincts, which count them immediately. Election Day ballots in 2020 generally supported Trump, although the Republican party has recently tried to encourage more of their voters to vote by mail.

The results will then likely change as mail-in ballots are counted, which takes time. As they are counted, you should expect to see Trump’s vote share decline and Harris’ share increase. That expectation is based on the voters who have requested mail-in ballots so far.

As of 10 a.m. on Oct. 28, 2024, data from the Pennsylvania Department of State indicated that 56% of the mail-in ballots requested at that point in Pennsylvania were from registered Democrats, about 32% from Republicans, with the remaining 13% from voters who did not register with a party or listed a third party. In 2020, over 6 in 10 mail-in ballots were requested by Democrats and about 1 in 4 by Republicans.

Be patient

Although conspiracy theories are prevalent in American politics these days, resist the temptation to believe unfounded claims. Such claims are often advanced by individuals or groups with a personal motivation to do so – to get more clicks or likes on social media, make money or gain political power.

American elections are administered by dedicated public servants on both sides of the political aisle who are observed by representatives from both political parties as well as nonpartisan watchdog groups. Academics and journalists across the nation also closely monitor elections and would be the first to ring the alarm if there were evidence of malfeasance.

Ballot counting in Pennsylvania will take time, and ultimately election officials have said they prioritize “accuracy over speed.” We will know the results of the election in time. Until then, be patient and watch one of the world’s oldest democracies at work.

Professor Safarpour has previously published articles on election administration, including a paper published in 2022 that used data provided by the State of Pennsylvania's Board of Elections in the 2016 election. Professor Safarpour did not consult with state election officials prior to the publication of this article and does not receive funding or support from any state government or board of elections for her research. The analysis presented here represents the best available data at the time of publication.