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As we know, the German Bundestag uses a mixed-member proportional (MMP) electoral system, with constituency votes that are majoritarian (299 seats) and party votes that are proportional (299 seats), plus the overhang and leveling seats.

What is the maximum number of seats there could theoretically be in the Bundestag?

Suppose CDU gets 100% of the vote in all constituency elections, and the SPD gets 100% of the vote in party votes. Or suppose that CDU wins all constituency elections with only 1% of the vote in each district, but all other parties got less than 1%. (I know that Germany has introduced a 5% threshold, but let's suppose there is no threshold.)

My impression is that the overhang seats would include as many as the seats that the number of constituency votes that need to be compensated (598+299=897). In this sense, the "proportionality" of the system counts the district majorities in tandem with the party proportion (i.e., 1/3 of seats are allocated to plurality of 1/3 of votes, and 2/3 of seats are given to the other 2/3 of votes).

Or is there no upper limit to the size of the Bundestag? In theory, if the parliament needs to have the same distribution as the proportion of party votes, then there could be an indefinite number of overhang votes.

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    If we just ignore whatever rules we don't want to deal with, there is no theoretical limit. The rule says 5% and using a lower nunber makes any calculation meaningless.
    – Nij
    Jul 3, 2023 at 20:45

1 Answer 1

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Since you are talking about overhang and leveling seats, you must be referring to the old election system which parliament replaced last month.

In the old system, everyone who gets the most votes in an electoral district is elected, and then additional seats are added until parliament is proportional to the party votes (where only parties with 3 directly elected members, or 5% of the vote, were considered).

If we assume candidate and party votes to be independent, the size of the Bundestag can become infinite: If everyone votes for the CDU candidate, but the SPD party, the SPD would get additional seats until it has 100% of parliament. In practice, everyone on the SPD list would be elected, however many people those are. And if you add more parties, it only gets worse.

If we assume candidate and party votes to align (which they aren't required to be, but probably often are in practice), and you have k parties, the Bundestag can reach 299 * k seats: Suppose all parties are equally powerful, except one party, who gets slightly more votes in every district. Then, that party gets all 299 direct mandates, but has only 1/k of the vote, so the Bundestag must grow to 299 * k to achieve proportional representation. If k = 19, every party still reaches the 5% threshold, a scenario which would result in 5681 seats.

That's why parliament changed the election law this year. The new election law entered into force on 14 June 2023 (with two constitutional challenges still pending), and achieves a fixed parliament size by weakening the direct mandates. Specifically, a candidate is only elected directly if

  • he has the most candidate votes in the district, and
  • his party has enough party votes to give him a seat

The second condition ensures that direct mandates can no longer skew the proportionality of parliament, and renders overhang and leveling mandates moot.

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  • Under the old rules, there would have been a hard limit by the number of candidates nominated by the party before the election. Once the list is exhausted, additional seats would be lost. The Pirate Party came close to that during Berlin state election, a decade or so ago.
    – o.m.
    Jul 4, 2023 at 3:56
  • I am surprised that the Bundestag's number of seats would be theoretically unlimited without the 5% threshold (and 5681 with it). In debates over election reforms, did people mention the fact that the size of parliament was in theory unlimited? It makes more sense to me to combine the district votes and party votes when calculating overhang seats, even if that does inject a modicum of majoritarianism into the system. It will be interesting to see how these reforms work out. Jul 4, 2023 at 8:34
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    The proposal to change the law starts with the following rationale: "The last elections to the German Bundestag have seen the number of deputies steadily increased (2013: 631, 2017: 709, 2021: 736), 123 percent of its legally stipulated size of 598 deputies. ... Even if this development cannot be extrapolated with complete certainty, a further increase in the size of the in future elections seems not only quite possible, but even probable. even probable. Model calculations know scenarios with over 900 deputies."
    – meriton
    Jul 4, 2023 at 13:46
  • That is, the were more concerned with the actual increase, rather than a theoretical one. For instance, after the newest election, there were too few physical seats in the parliament building to seat all delegates, so some delegates had to sit on the spectator stands while parliament statt installed additional seats :-)
    – meriton
    Jul 4, 2023 at 13:55
  • As for transitioning to a mixed majoritanism system, the proposal justifies its solution by writing: "In its decision (BVerfGE 131, 316, 2. Ls., 359 ff. [2012]) the constitutional court has identified proportionality as the "essence" of the current election system. This propsal consistently pursues this principle by ...".
    – meriton
    Jul 4, 2023 at 14:19

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