There will be 709 seats in the Bundestag.
709
That means 111 overhang and balance seats.
111 is insane, that has to be a record, right?
What's the maximum possible number of overhang/balance seats? Like is there even a legal limit? If not, what is the largest theoretically possible size the bundestag can get?
One might be able to determine a practical maximum size under circumstances similar to the present (too not-so-big big parties and several smaller parties). It might not be possible to squeeze in additional smaller parties without some failing the 5% threshold.
So adopt a simple model where some CDU/CSU voters stay home, and assume that this is consistent across the country (percentage of CDU/CSU voters would decrease by a percentage, rather than percentage of total voters).
The CDU/CSU plurality can be calculated for each constituency, expressed as a percentage of the CDU/CSU vote in the district, and the districts arranged from smallest to largest plurality.
Then district by district reduce the CDU/CSU percentage such that they lose one additional direct seat, while losing some percentage of their overall popular vote. The real determinate is whether they lose direct seats faster than their popular vote declines or vice versa.
We could also do the inverse, increasing the CDU/CSU percentage so that they gain additional direct mandates.
An alternative analysis might vary the SPD percentage in a similar fashion.
The key factor in expanding the Bundestag is a relatively low share of the votes for CDU/CSU, but at the same time a massive lead relative to the SPD. If they were closer together, there would fewer CDU/CSU direct mandates.
