Former Chicago Public Schools CEO Paul Vallas and Cook County Commissioner Brandon Johnson face off in the city’s runoff election for mayor on Tuesday, vying to replace outgoing incumbent Lori Lightfoot.

Vallas has positioned himself as a moderate and has the backing of the Chicago police union and major business groups. Johnson is a former teacher and union organizer backed by the Chicago Teachers Union.

Vallas finished first and Johnson was second in the February municipal election, which proceeded to a runoff because no candidate received over 50% of the vote. Lightfoot was eliminated from contention after placing third.

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Here’s a look at what to expect on election night:

Election Day

Polls close at 8 p.m. ET.

How Chicago Votes

Voting is open to all voters, who can register on election day.

The AP will declare a winner in the race for Chicago mayor. The AP will also tabulate 14 races for Chicago alderperson but will not call winners in those races until after the results are certified.

In the February election, the AP first reported results in Chicago at 8:19 p.m. ET. The final election night update for overall results came just after 12 a.m. ET, with 90% of votes counted. Election officials separately released ward-level results, a process that continued until about 2 a.m.

Brandon Johnson/Paul Vallas

Mayoral candidates Brandon Johnson, left, and Paul Vallas, on Jan. 23, 2023, in Chicago. Chicagoans will vote Tuesday on which of the two Democrats will replace outgoing Mayor Lori Lightfoot. (Chicago Tribune/Getty Images)

Decision Notes

The AP does not make projections and will only declare a winner when it’s determined there is no scenario that would allow the trailing candidates to close the gap.

Should a candidate declare victory or offer a concession before the AP calls a race, we will cover newsworthy developments in our reporting. In doing so, we will make clear that the AP has not yet declared a winner and explain why.

The board of elections doesn't expect to release ward-level results until around 1 a.m. Before those results are released, the AP will analyze each update in the citywide vote count to see if either candidate has a big enough lead to withstand late-counted votes in areas that may support the trailing candidate.

Once ward-level results are released, the AP will analyze how the candidates are doing in the areas they won in the February election, when Vallas carried the city’s northwest and southwest wards and Johnson carried the northeast part of the city. The AP will also analyze how the candidates are doing in wards that were won by Lightfoot and Jesús 'Chuy' García in the February election, to see if there is any path for the trailing candidate to catch the leader.

The AP may call a race in which the margin between the top two candidates is 0.5% or less, if we determine the lead is too large for a recount and legal challenge to change the outcome. In Illinois, there are no automatic recounts. Trailing candidates can request recounts if they receive at least 95% of the total votes of the winning candidate.

However, recounts in Illinois are for the purposes of legal discovery only and cannot by themselves change the results of an election.

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Q: What Do Turnout and Advance Vote Look Like?

A: As of Feb. 28, there were 1.6 million registered voters in Chicago. As of Sunday, 246,188 voters had cast advance ballots.

In the February election, 52% of Chicago voters cast their ballots before election day. Mail-in ballots can arrive as late as April 18 and be counted so long as they are postmarked by election day.

Q: How Long Does Counting Usually Take?

A: Chicago counts a significant number of votes after election day, which could delay race calls in a competitive election. In the February election, the city counted 10% of ballots after election day.

Election officials said they plan to start releasing citywide results shortly after polls close at 8 p.m. ET. However, they don’t expect to start releasing results by ward until around 1 a.m. ET.

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Following election day, the Board of Elections plans to update results several times each day on Wednesday and Thursday, and then periodically through the April 18 deadline to receive mail ballots.