How long will it take to get Pa. election results? It depends. Here’s what you need to know.

We might be in for a days-long wait for Pennsylvania election results, à la 2020. Or not. It’s complicated.

Most Pennsylvania votes will be counted on election night, with the vast majority tallied by sometime Wednesday. That will leave just small batches of votes left to count across the state in the following days.

But if Pennsylvania’s high-stakes U.S. Senate race is as close as expected, the outcome could hinge on those last votes.

And that could put a national spotlight on Philadelphia in particular.

City officials voted Tuesday morning — as polling places opened — to reinstate a time-consuming and labor-intensive process for catching double votes that will slow how quickly they can report results. That shift, which came in response to a Republican lawsuit, threw a wrench into what was nevertheless still poised to be a faster vote count than two years ago.

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Pennsylvania’s votes will still take days — weeks, really — to fully count, as they do every election. But there are some changes this year that will speed up the vote counting and reporting. Counties are better at it now than they were in 2020, when it took until Saturday morning for news organizations to declare a winner in the presidential race. And there will be fewer mail ballots to tally.

So most votes will be reported within just a few hours of polls closing at 8 p.m. on Nov. 8, and the vast majority should be counted by sometime Wednesday.

That means there’s a decent chance that some of the biggest races are called on election night or shortly after — unless the margins are so tight that it comes down to the final, slower-to-count votes.

For those races, it might feel more like what we were used to before the 2020 expansion of mail voting, when races were called quickly. But the rise of mail voting has fundamentally changed how ballots are cast and counted — and will affect this election, too.

Whatever happens — and whenever races are called — it will still take time to count every vote, as it always has.

“We must again ask for patience,” Leigh Chapman, Pennsylvania’s acting secretary of state, told reporters. “An accurate count of all eligible votes is paramount, and it cannot be rushed.”

The Inquirer has been covering the vote-counting process as it’s changed in recent years, and we talked to more than a dozen elections officials across the state to understand how they’re running things this year. Here’s what we expect to see as results stream in on election night — don’t forget the “blue shift” from 2020 — and key things to know about how votes are counted and races are called.

Winners are official only after elections are certified, which in Pennsylvania happens 20 days after Election Day. But news organizations declare winners long before that. (The Inquirer relies on the Associated Press for that.)

Those calls are made using sophisticated statistical models that look at partial results to identify the winner.

The margin between candidates is key to that.

Sometimes races can be called quickly, as in this year’s Democratic primaries and the Republican primary for governor: Those candidates all won handily, and partial results quickly made clear they would.

Close races take more time.

Pennsylvania is a very evenly split battleground state, giving Donald Trump a win in 2016 by less than 1% of the vote, and Joe Biden in 2020 by just more than 1%.

Some races are so close that they trigger an automatic recount. Remember how we didn’t know that Mehmet Oz had beaten David McCormick in the Republican Senate primary for a while? It wasn’t until 2½ weeks after Election Day that McCormick conceded as it became clear during the recount that he lost.

Current polling shows a strong lead for state Attorney General Josh Shapiro, the Democratic nominee for governor, over State Sen. Doug Mastriano, the Republican. If that holds true in the actual vote, it could mean a fairly easy and early declaration of a winner.

The Senate race seems likely to take more time: Polling suggests that Oz, the Republican, and Lt. Gov. John Fetterman, the Democrat, may end up within just a few percentage points of each other.

To use partial results to model the outcome requires having enough votes to clearly see the patterns and how they play out across different places and demographics.

For example, you need results from politically different areas to tell how things are going overall — a heavily Democratic, Black neighborhood in Philly might not tell you much about how a deeply Republican, white rural area is voting.

Those results take time. Counties run elections, which means Pennsylvania’s 67 counties have 67 slightly different ways of doing things.

The in-person votes cast on Election Day are the fastest to count and report. Voting machines keep running totals throughout the day and store them on USB drives. After polling places close, workers take those to the county elections office, where results from the machines are quickly uploaded. Nearly all results from polling places are reported within a few hours.

It’s the mail ballots that really take time.

» READ MORE: Philly’s mail ballot drop boxes are open for the midterm elections. Here’s how to use them.

Elections workers have to check the mailing envelopes to make sure requirements are met, such as ensuring voters signed them. Workers open the mailing envelopes and remove the ballots, which are inside second “secrecy” envelopes. Then they open that second envelope and remove the ballots, unfold them, flatten them, and, finally, run them through high-speed scanners that read and count them.

It’s a slow process with various things that can slow it down, such as when a ballot has to be taken out and rejected.

Philadelphia elections officials had originally expected to have nearly all votes counted by Wednesday morning. But their vote Tuesday to reinstate what’s known as poll book reconciliations means that ballots still left to count after Tuesday night — numbering in the low tens of thousands — will instead be counted and reported in a slow trickle over the rest of the week.

» READ MORE: Philly elections officials adopted a last-minute change that will slow down the counting of votes

Elections officials across Pennsylvania have been calling since 2020 for the legislature to let them begin the process earlier (state law prohibits it from starting until 7 a.m. Election Day). Starting what’s known as “pre-canvassing” earlier wouldn’t make the actual vote count faster, but starting it earlier would end it earlier.

Democrats are still much more likely to vote by mail than Republicans because of Trump’s relentless attacks on mail ballots. That means in-person results are more Republican than the overall vote — and mail results are more Democratic.

That affects how we learn about the results.

When polls close at 8 p.m. and counties are allowed to begin reporting results, the first numbers are the mail ballots counted throughout the day. That means the first votes reported lean much more Democratic, so it may briefly seem that Democrats have a strong lead. But that’s only a fraction of the vote.

Counties then continue to count mail ballots, but the overwhelming number of votes being reported for the next few hours are the in-person ones. And because those are more Republican, it will seem that an initial Democratic lead suddenly becomes a Republican advantage that, by early Wednesday morning, might seem hard to overcome.

But as the rest of the mail ballots are counted and reported, the total will continue to shift more toward Democrats.

That’s called the “blue shift.” We saw it in 2020, when Trump appeared to have a strong lead on election night — and then the counting of mail ballots slowly eroded and then flipped that lead.

There are a few reasons why votes should be counted a lot faster this year — barring something unexpected.

For one, turnout almost certainly won’t reach the levels of the presidential election. And the percentage of votes cast by mail has decreased since 2020, when the pandemic led many people to use mail ballots.

Most votes will be cast in person. And a significant portion of mail ballots will be counted during Election Day and reported shortly after 8 p.m. So a big majority of results will be known by early Wednesday morning.

Counting mail ballots is also faster than before because counties are better at it — they have more equipment and experience, and they know how to set up and staff the process.

And this year, a new law requires counties that receive state election grants to count ballots “without interruption” until they’re done. Almost every county applied for that money, which means they won’t be stopping at the end of the night and resuming in the morning. (Counties are also required to report at midnight the number of mail ballots left to count, which could help us better understand the remaining vote count.)

» READ MORE: Philly might scale back a process for catching double votes — because of GOP ‘election integrity’ rules

Many if not most of the 67 counties will likely be done by the early morning hours Wednesday. Elections officials in small counties said their mail ballots won’t be a big burden.

The biggest counties have some experience with around-the-clock vote counting, having done it in 2020, and officials said they’re preparing. Montgomery County, for example, expects to be almost entirely done counting mail votes on election night.

As counties wrap up their mail ballot counts, the only votes left will be small batches that take days to figure out. Those include ballots with some sort of problem that elections boards must decide how to handle, ballots that have to be recreated because they won’t scan properly, provisional ballots, and overseas and military ballots.

But those ballots represent a tiny fraction of the vote.

The vast majority of votes will be quickly counted and reported. Some of the same phenomena we’ve seen in the past will be repeated — such as the “blue shift” as mail ballots are counted — but most of that should happen over a shorter time period, making it less noticeable.

The blue shift will also likely be smaller than in 2020, since the use of mail ballots has decreased.

And as usual, how quickly races are called depends both on how quickly votes are counted and how close races are.

If a race hasn’t been called Wednesday morning, it probably just means it’s a very close contest.