Related question on Metaculus:

Will the Chancellor of Germany following the next election be from the CDU/CSU union?

The German electoral system sets the size of the Bundestag (national parliament) to at least 598 members. Due to the peculiarities of the voting system, especially the split between first vote (first past the post) and second vote (proportional representation), the 5% electoral threshold and split votes resulting in excess mandates, the size of the next Bundestag is to be projected to have up to 1000 members (link in German, translation below)

Next Bundestag could have more than 1,000 deputies Since the 2017 election, the Bundestag has had 709 members - more than ever before. But even this number could be significantly exceeded after the vote in September.

Berlin (dpa) - The next Bundestag could be a good 1000 MPs strong, according to calculations by electoral law expert Robert Vehrkamp.

"The range of plausibly possible Bundestag sizes runs from about 650 to more than 1,000, and we can't rule that out," the Bertelsmann Stiftung expert told the Deutsche Presse-Agentur in Berlin. He is also a member of the commission set up by the Bundestag to reform electoral law and modernize parliamentary work.

The standard size of the Bundestag is 598 seats. Since the 2017 election, it has 709 deputies - more than ever before. Although the CDU/CSU and SPD pushed through an amendment to the electoral law last October, experts believe that this will hardly lead to the hoped-for reduction in the size of parliament.

[…] According to Vehrkamp's presentation, it is not possible to make an accurate prediction about the size of the next Bundestag. "What is often overlooked in the discussion: It depends not only on the second vote result. It depends at least as much on vote splitting how many overhang mandates there will be. And splitting behavior is even more incalculable than the allocation of second votes."

For example, the Greens could get about twice as many second votes as in the 2017 election. "But we don't know what the splitting behavior of Green voters will look like then." If about 20 percent of them were to give their first vote to the CDU/CSU - for old ties, for example - that would have "an enormous leverage effect," Vehrkamp said. "Then, depending on the scenario, you're quickly at 880, 950 or, in extreme cases, even over 1,000 mandates. It doesn't have to happen that way, but it is possible. The current electoral law is a real game of vabanques with regard to the size of the Bundestag."

Vehrkamp calculated the size of the Bundestag from the ARD "Deutschlandtrend" of August 5 (CDU/CSU: 27 percent, Greens: 19, SPD: 18, FDP: 12, AfD: 10, Left: 6) with three different splitting scenarios. Depending on the scenario, it comes to 695, 851 or 978 deputies. […]

How many members will the next Bundestag have?

The question will resolve with the number of members listed on the website of the German Bundestag following the final results of the September 26, 2021 federal elections.

If no Bundestag is formed following the elections, the question will resolve ambiguously.