Winner's bonus (seats vs votes)
How much first-past-the-post over- or under-rewards a party.
How it's calculated
Party seat share minus party vote share, at council level, in pp.
Worked example
Heworth May 2023: Labour won 100% of the 3 seats on 64.3% of the vote, a ward-level bonus of 35.7pp. Council-level figures appear once composition data is loaded.
Source: Heworth ward, City of York — by-election of 15 January 2026 and May 2023.
Caveats
- Most meaningful across a whole council, not a single ward.
Where it's used
Other definitions
Vote shareChange in shareSwing (two-party, Butler)MajoritySwing needed to gainUncontested seatCandidates per seat / per wardContestation rateWinner's shareEffective number of partiesIncumbency and re-election rateWomen candidates and councillorsTurnout (three methods)Council control and No Overall Control (NOC)Majority at riskPsephology National Share EstimateBy-election vote trackerNotional resultIndex of changeSplit-ticket indicatorNational Equivalent Vote