The Senate is elected by the twelve provincial states, the constituencies of Bonaire, Sint Eustatius and Saba, and a new constituency which votes on behalf of the Dutch abroad. A total of 616 members, all voting at the same time, vote at 3pm on Tuesday.
Each vote is worth a certain number of points, depending on the number of inhabitants. For example, a vote in South Holland is worth 692 points, while a vote for Saba is worth 4 points. In total there are 178,970 points to distribute. For a seat in the Senate you need 2386.27 points.
Not required
Members of Parliament are not obliged to vote for their party. The system makes horse trading possible. Parties sometimes have votes to spare. They can give it to others without costing them a place. That space is, among others, with the party Independent Political Netherlands (OPNL). The regional parties work together in this and sometimes negotiate with the BBB about participation in the provincial coalition. OPNL has practically one seat in the Senate. Regionals can afford to lose, for example, two votes in Zeeland, one in North Brabant and one in Drenthe.
Parties like PVV and JA21 have even more leeway. If the BBB manages to win enough votes from other parties in this way on Tuesday, it could eventually win a seat in the Senate.
What can work for the BBB can obviously work for other parties as well. For example, D66 can help the VVD or the ChristenUnie, and thus the coalition, with an extra seat. The CDA in turn can help prevent D66 from losing a seat as a result.