Overhang Seat

An overhang seat (German: Überhangmandat) occurs in mixed-member proportional (MMP) electoral systems when a party wins more direct constituency seats than its share of the proportional (party-list) vote would entitle it to. Because the constituency winners keep their seats, the legislature expands beyond its nominal size to accommodate the extras.

The phenomenon is most closely associated with Germany's Bundestag, where voters cast two ballots: one for a local candidate (Erststimme) and one for a party list (Zweitstimme). The party-list vote determines each party's overall share of seats; constituency wins are then deducted from that allocation. If a party wins, say, 25 constituency seats but is only entitled to 20 under proportional allocation, it retains five overhang seats.

Overhang seats became politically contentious because they distorted proportionality, advantaging large parties (historically the CDU/CSU and SPD) that won many direct races. In a 2012 ruling, Germany's Federal Constitutional Court (Bundesverfassungsgericht) held that uncompensated overhang seats violated the principle of equal suffrage when they exceeded roughly 15 mandates. The Bundestag responded with the 2013 electoral reform introducing Ausgleichsmandate (leveling or balance seats) awarded to other parties to restore overall proportionality. This caused the Bundestag to balloon — the 2021 election produced 736 members, well above the nominal 598.

A further reform passed in 2023 under the Scholz government sought to cap the Bundestag at 630 seats by abolishing both overhang and leveling seats; constituency winners from parties exceeding their proportional entitlement would no longer be seated. The Federal Constitutional Court partly upheld this reform in July 2024 while striking down a related provision on the 5% threshold.

Overhang seats also appear in other MMP systems, including New Zealand's parliament and the Scottish Parliament and Welsh Senedd, though their effects there are typically smaller.