The big day is finally here—Election Day 2020 has arrived! Many have been waiting for this day for the last four years, and for many more, this day will be filled with both a mixture of hope and anxiety. But we’ve got some bad news for you—anxiety might get the bigger share of your emotions today. That’s because it’s possible—even likely—no clear winner will be announced even hours after the polls have closed in all 50 states.

Why? Because even in a normal election year (and this election year is far from the norm) officially tabulating all the votes cast for president of the United States always takes weeks. I know what you’re thinking: “But on many election nights past, the networks have called a winner that night.” The thing is, when a network—be it Fox News or MSNBC—”calls” an election, they are really just making a projection—that is, an educated guess which candidate is likely to win based on all the data they have at the time.

When an election is a landslide—with one candidate clearly getting the lion’s share of the votes—networks have confidence calling the election relatively soon after polls close, usually the same night. But even then, all the ballots cast will not have been counted, and they won’t all be counted for weeks after Election Day. That means, if the data after the polls close show the election is a tight race, it can be days before an election is called for one particular candidate, and weeks before all the votes cast are fully counted.

As Slate notes in an interesting article about why President Trump can’t just declare victory, “no state fully counts their ballots on election night. Returns are unofficial and always contain errors. Many states allow military ballots to arrive for days after Election Day. Counting generally continues for days and weeks after Election Day, and results are not certified until weeks after.”

The fact that tens or even hundreds of thousands of votes still need to be counted long after Election Day is over is why you might see terms like “red mirage” or “blue mirage” thrown around later today. Here the colored “mirage” refers to early results that look to heavily favor one candidate over the other—sometimes by a huge margin. But as the days continue and more of the outstanding ballots are counted, those results can shift so much that the other candidate takes the lead.

As CNN notes, you should expect to see several blue mirages and red mirages in specific states in the early hours after the polls close today. However, don’t be surprised if those early results shift radically in the other party’s favor as the hours and days go by.

So, while it’s possible for there to be enough data late tonight or by early tomorrow morning to confidently call the election for one candidate or the other, it’s just as likely that we may not know who won for days or even weeks until all the votes can be tabulated (check out The Brennan Center for Justice’s in-depth explainer to understand just how long votes in varying states can take to be counted after Election Day for more information). In short, expect your anxiety to bounce around like a ping-pong ball, not just tonight—but potentially for days to come as all the ballots cast continue to be counted long after the polls have closed.