When will we actually know who won Congress?

When the outcome of Tuesday's election will become clear is anyone's guess, even though what is at stake – which party ends up controlling Congress – could hardly be clearer.

The Associated Press will call races in all 435 House districts this year, along with the 35 Senate contests up for election.

Control of the House comes down to which party reaches 218 seats.

Republicans currently have the edge, with 219 members caucusing with the party – just one more than the minimum needed for a majority when all seats are filled.

There are two vacancies now.

In the Senate, the bar is 51 seats for Democrats or 50 for Republicans, because Vice President JD Vance can cast a tie-breaking vote for his party.

Republicans hold a 53-47 edge in the Senate right now.

In 2022, it took over a week before the House was called

The pace of past calls offers a rough guide. During the 2022 midterm elections, the AP called control of the Senate four days after Election Day, while the House call came eight days later.

The 2024 presidential cycle saw a bigger gap between the two, with Senate control called the day after Election Day and the House call coming eight days later.

Some states consistently take days to count all their ballots.

California, the nation's most populous, has seen thousands of mail ballots dropped off on Election Day.

In 2022, the state counted half its votes after Election Day.

Other states, including Alaska and Maine, use ranked-choice voting, and both have key Senate races this year.

Under that system, a candidate can win outright with more than 50% of votes in the first round.

If no one reaches that threshold, the candidate with the fewest first-choice votes is eliminated, and their votes are redistributed to voters' second choices.

The process can significantly delay results.

The AP does not make projections and will declare a winner only when it determines no scenario would allow the trailing candidates to close the gap.