🏛️ UK Parliamentary Seat & Vote Pivotality Simulator

First-Past-The-Post swing model, tactical voter leverage & disproportionality analysis
Majority Status
Labour Majority (2 seats)
326 / 650 threshold
Gallagher Index
14.82
Disproportionality Rating
Key Swing Constituency
Hendon (Margin: 124 votes, Pivotality Index: 9.8/10)
Most vulnerable seat determining government formation
650 SEATS ALLOCATION Lab: 326 | Con: 198 | LD: 52 | Reform: 24 | SNP: 28 | Green: 2 | Oth: 20
326 MAJORITY
Lab
Con
LD
Reform
SNP
Green
Other
Constituency Inspector & Pivotality Breakdown
Constituency Region Winner Runner-up Margin Pivotality Score

How FPTP Pivotality Math Works

First-Past-The-Post creates extreme vote-to-seat disproportionality. The Gallagher Index measures the divergence between national vote percentage and seat percentage (0 = perfect PR, >15 = severe distortion). The Voter Pivotality Index evaluates the relative individual power of a single vote: voters in hyper-marginal swing constituencies (low winning margin) exert vastly greater influence over government formation than voters in safe seats.

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