When will we know the results?

Millions of Americans are voting in midterm elections. The outcome determines which party - US President Donald Trump's Republicans or opposition Democrats - controls Congress and could have a significant impact on Trump's presidency.

Once polls close, it is possible the results will not be projected for several hours, days or even weeks. Here's what you need to know.

When will we know the results and who controls Congress?

Congress is made up of two parts - the lower chamber, the House of Representatives and the upper chamber, the Senate.

To win a majority in the House, a party needs 218 seats. In the Senate, a party needs 51 seats for an outright majority. But if the upper chamber is split 50-50, the vice-president has a tie-breaking vote, which gives their party control of it.

First results will start to come in after 18:00 EST (23:00 GMT). They won't tell us much about the overall result because these races are in places considered safe bets for Republicans (Kentucky and Indiana) or Democrats (Vermont).

Throughout the night, BBC analysts will focus on the competitive races which will give an indication of how well things are going for Trump.

There are several tight Senate contests in the Eastern Time zone - like Ohio, where polls close at 19:30 EST (00:30 GMT) and Maine, where they shut at 20:00 EST (01:00 GMT). These could provide early indications of the electorate's mood.

Some key contests might start to be "called" by US media outlets. They use models to project which way a state has voted, even before the full vote count has been completed.

This happens when they believe a party or a candidate has gained a lead that cannot be beaten. But in some closely-fought states, outlets could take a long time to make their projections.

The overall timing of the result will depend on how tight the races are and which races end up being decisive.

When did we know the results in 2022?

In 2022, Republicans and Democrats were still in a tight race for control of the US Congress on 9 November, a day after the midterms.

While Republicans were favourites to win the House of Representatives, the fight for the Senate remained on a knife-edge.

The full picture took several days. CBS News projected Republicans had secured the 218 seats needed for a majority in the House on 17 November.

Counting in a crucial Senate race in Nevada took four days. The Democrats' narrow victory in the state brought them to 50 seats, allowing them to retain control of the Senate because then Vice-President Kamala Harris held a tie-breaking vote.

Georgia's Senate contest had to be settled by a run-off election because no candidate passed the 50% mark in November.

The results were not available until 7 December, when Democrats won this seat.

What are the key races to watch in 2026?

There are seven Senate races deemed to be a toss-up by independent elections analyst Cook Political Report, external - Alaska, Kansas, Iowa, Maine, Michigan, Ohio and Texas.

Of these, six are currently held by Republicans and one by Democrats. The Democrats would need to win four of those seats, plus four classed as likely or leaning Democratic, to hit 51 and take control of the Senate.

If Democrats fail to keep hold of their seat in Michigan, winning a majority in the Senate becomes much harder. Abdul El-Sayed, a left-wing political outsider, is up against Republican rival Mike Rogers, a Trump ally and former FBI agent.

But polls have suggested they have a chance even in Texas where former teacher James Talarico could become the first Democrat to win a Senate seat in the state since 1988 if he defeats Ken Paxton, the current state attorney general and close Trump ally.

The current Republican majority in the House, the lower chamber, is thin. They have 218 representatives, the exact number needed to have control, plus one independent who votes with them.

Some of the most closely-watched races in the House are in east-coast states, according to the Cook Political Report. These include New York's 17th District, Pennsylvania's 8th District and Virginia's 1st District.

When do polls close?

The results of a voter poll will be released at 17:00 EST (22:00 GMT), which will give us an indication of the issues at the forefront of voters' minds.

Then, at 18:00 EST (23:00 GMT), the first polls close in Kentucky and Indiana. After that, all eyes will be focused on the seven key battleground states:

• 19:30 EST (00:30 GMT) - Polls close in Ohio, where Republican Senator Jon Husted finds himself neck-and-neck with Democrat Sherrod Brown. Results from this state could give us a clue as to how the night might unfold

• 20:00 EST (01:00 GMT) - Voting ends in the tight Senate race in Maine between Republican Senator Susan Collins and Democrat Troy Jackson and in most of Michigan, Kansas and Texas

• 21:00 EST (02:00 GMT) - Polls close in Iowa and the remaining parts of Michigan that sit in the Central Time Zone, as well as Kansas and Texas. In the hours that follow, a picture might start to emerge of whether things are going to plan for the Republicans - or the Democrats

• 01:00 EST (06:00 GMT) - Voting ends in Alaska, the last battleground state. A close Senate race between Democrat Mary Peltola and incumbent Republican Senator Dan Sullivan has been making headlines over the inclusion of a second candidate named Dan Sullivan on the ballot

How does the vote-counting work?

Each state administers its own elections and has its own rules for counting and processing votes.

The order of which votes are tallied first varies from state to state. Some states, like Florida, process early and mail ballots prior to election day, while others only begin tabulating on 3 November.

Local election officials - sometimes appointed, sometimes elected - verify, process and count individual votes, in a process known as canvassing.

Most states require a formal post-election audit that involves a manual count of ballots checked against machine totals, although rules vary across the country. Full hand counts are generally reserved for recounts.

Every state and locality has rigorous rules which specify who can participate in the canvass, the order in which votes are processed and which parts are open to the public, including how partisan observers can watch the count and, in some states, raise formal challenges.

What might cause a delay?

Tight races will take longer, and create the possibility of recounts being triggered and legal challenges.

Mail-in ballots take considerably longer to count, as officials need to process envelopes and verify signatures.

More than 30 states allow ballots to be processed before election day, but other states do not, meaning that it may take days to get results.

In California, all ballots must be posted before or on election day and will still be counted if they arrive within seven days of the election.

As every state has its own rules and policies, some delays could be built-in to the system.

In Alaska, ranked-choice voting could mean that tabulations take considerably longer than elsewhere in the country and the controversy over ballots could mean that legal challenges can complicate things.

What happens if results are challenged?

Once every vote has been included in the final results, and after processes such as recounts have been completed, the election results are certified - first at the local, county, level. The results are then certified state-wide, usually by a state canvassing board of the secretary of state.

The governor then typically signs the certifications for House and Senate winners to be sent to Congress.

Results can be challenged. Recounts can be requested by candidates in close races, and in some states recounts are automatically triggered if they fall within a certain margin.

Additionally, candidates can file legal election contests alleging irregularities.

Congress has the final word. Losing candidates in both House and Senate races can file contests, with slightly different processes in each of the two chambers.

Both chambers can, theoretically, refuse to seat someone or order an investigation.