When will we know the results?

The first polls have closed in the US midterm elections, which will shape the rest of Donald Trump's presidency. The outcome determines which party - Trump's Republicans or opposition Democrats - controls Congress.

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

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.

The first results to come in 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.

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.

Polls have suggested Democrats have a chance 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.

Democrats also need to keep hold of their seat in Michigan, where Abdul El-Sayed, a left-wing political outsider, is up against Republican rival Mike Rogers, a Trump ally and former FBI agent in a closely-observed race. The state was initially classified as a "toss-up" by Cook Political Report, but was reclassified as "leans Democrat" the day before the vote.

The current Republican majority in the House, the lower chamber, is thin. They have 218 representatives, 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.

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 and then state-wide.

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.

Candidates can also 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.