The U.S. presidential election will be decided by about a dozen states that could swing to either President Donald Trump, a Republican, or Democratic challenger Joe Biden.

These states will play a critical role in delivering the 270 Electoral College votes needed to win the White House. Due to a surge in mail voting amid the coronavirus pandemic – as well as the states’ varying rules for when ballots can be counted – the results may not be known on Tuesday’s Election Day.

GEORGIA

Electoral votes: 16

Polls have closed, except for Spalding County, where all precincts remain open until 9 p.m. EST.

Rating in presidential contest: Toss-up

Other key races: Both U.S. Senate seats are up for grabs and considered competitive.

Vote counting: Georgia has no-excuse absentee voting. Ballots must be received by clerks by the close of polls on Election Day. Ballots can be opened and scanned on receipt, but they cannot be tallied until after the polls close on Tuesday. Officials in Fulton County, home to Atlanta and a tenth of all Georgians, warned on Tuesday that a final vote count would take longer than expected after a burst pipe delayed absentee-by-mail ballot processing for four hours, according to local reports.

FLORIDA

Electoral votes: 29

Polls have closed.

Rating in presidential contest: Toss-up

Other key races: Competitive U.S. House of Representative races in the 15th and 26th Districts

Vote counting: Florida has no-excuse absentee voting. Election officials can begin scanning ballots more than three weeks before Election Day, but results cannot be generated until after polls are closed. All ballots must be received by the close of polls on Election Day to be counted. Ballots flagged for signature errors can be corrected, however, until 5 p.m. on Thursday.

NORTH CAROLINA

Electoral votes: 15

Polls have closed.

Rating in presidential contest: Toss-up

Other key races: Competitive governor and U.S. Senate contests

Vote counting: North Carolina has no-excuse absentee voting. Absentee ballots can be scanned weeks in advance, but results cannot be tallied before Election Day. In a blow to Trump, the U.S. Supreme Court declined last week to block the state’s plan to tally ballots that are postmarked by Tuesday and arrive by Nov. 12.

NEW HAMPSHIRE

Electoral votes: 4

Polls have closed.

Rating in presidential contest: Leans Democratic

Other key races: Governor Chris Sununu, a Republican, looks poised to win re-election.

Vote counting: New Hampshire state officials have said all voters are able to cast an absentee ballot if they have concerns about COVID-19, and the ballots must be received by 5 p.m. on Election Day. Ballots could be pre-processed in some jurisdictions beginning on Oct. 29, but not counted until the polls have closed on Tuesday.

OHIO

Electoral votes: 18

Polls have closed.

Rating in presidential contest: Toss-up

Other key races: Competitive U.S. House contest in the 1st District

Vote counting: Ohio has no-excuse absentee voting. Ballots could be scanned, but not tallied, as early as Oct. 6. Absentee ballots are the first to be counted on election night. Mail ballots had to be postmarked by Monday and received by 10 days after Tuesday’s election to be counted.

MICHIGAN

Electoral votes: 16

Polls have closed, except for four counties bordering Wisconsin that close at 8 p.m. CST.

Rating in presidential contest: Leans Democratic

Other key races: Competitive U.S. Senate contest

Vote counting: Michigan has no-excuse absentee voting. Ballots must arrive at clerks’ offices by the close of polls on Election Day. Some densely populated jurisdictions in the state, such as Detroit, began sorting absentee ballots on Monday, but the vast majority did not. Clerks can begin scanning and counting absentee ballots at 7 a.m. on Tuesday.

PENNSYLVANIA

Electoral votes: 20

Polls have closed.

Rating in presidential contest: Leans Democratic

Other key races: Competitive U.S. House contests in the 1st and 10th Districts

Vote counting: Pennsylvania has no-excuse absentee voting, and ballot counting can begin at 7 a.m. on Election Day. Last Wednesday, the U.S. Supreme Court let stand a ruling by Pennsylvania’s top court that officials in the state can accept mail-in ballots three days after Tuesday’s election, so long as they were postmarked by Election Day.

TEXAS

Electoral votes: 38

Polls have closed, except in two western counties in Texas where they close at 8 p.m. CST.

Rating in presidential contest: Toss-up

Other key races: Competitive U.S. Senate contest

Vote counting: Texas voters must qualify to vote by mail, for example by being older than 65, being ill or disabled, or not being present in their voting county during the early voting period through Election Day. All voters can vote early in person. The population of a county determines when election officials can pre-process and count mail ballots. If the county has more than 100,000 people, the ballots may be counted after polls close on the last day of in-person early voting in the state, which was Oct. 30. Ballots will still be counted if they are postmarked by Tuesday and received by 5 p.m. the day after the election. For military and overseas voters, that deadline is extended through the end of business on Nov. 9.

WISCONSIN

Electoral votes: 10

Polls close: 9 p.m. EST (0200 GMT Wednesday)

Rating in presidential contest: Leans Democratic

Other key races: No governor or U.S. Senate races on the ballot

Vote counting: Wisconsin has no-excuse absentee voting. The state’s election officials cannot count mail-in ballots that arrive after Election Day, the U.S. Supreme Court ruled on Oct. 26. Ballots cannot be counted until polls open on Tuesday.

MINNESOTA

Electoral votes: 10

Polls close: 9 p.m. EST

Rating in presidential contest: Leans Democratic

Other key races: Competitive contests for the U.S. Senate and U.S. House in the 1st and 7th Districts

Vote counting: Minnesota has no-excuse absentee voting, and ballots must be pre-processed within five days of receipt. Beginning on Oct. 20, ballots could be opened and logged, but the results are only tabulated after polls close on Election Day. A federal appeals court ruled last week that the state’s plan to count absentee ballots received after Election Day was illegal.

ARIZONA

Electoral votes: 11

Polls close: 9 p.m. EST

Rating in presidential contest: Leaning Democratic

Other key races: Competitive U.S. Senate contest

Vote counting: Arizona has no-excuse absentee voting. All ballots must arrive by the close of polls on Election Day. Ballots could be scanned and tabulated starting 14 days before Tuesday but results not reported until after polls close on Election Day.

NEVADA

Electoral votes: 6

Polls close: 10 p.m. EST (0300 GMT Wednesday)

Rating in presidential contest: Leans Democratic

Other key races: No governor or U.S. Senate contests on the ballot

Vote counting: Nevada has no-excuse absentee voting, and ballots can be processed upon receipt. Nevada officials could begin scanning and recording ballots 14 days before the election, but results are not released until election night. Ballots postmarked by Tuesday will be counted so long as they arrive within seven days after the election.

IOWA

Electoral votes: 6

Polls close: 10 p.m. EST

Rating in presidential contest: Toss-up

Other key races: Competitive U.S. Senate contest

Vote counting: Iowa has no-excuse absentee voting. The ballots must be received by the close of polls on Election Day, or by noon the following Monday if they were postmarked by Nov. 2. Election officials were allowed to begin opening ballot envelopes on the Saturday before the election and begin scanning and tabulating them on Monday.

Reporting by Michael Martina; Editing by Colleen Jenkins, Peter Cooney and Sonya Hepinstall