Traders assign the highest probability to exactly six UK parliamentary by-elections in 2026, reflecting a modest number of vacancies created by resignations and other triggers since the 2024 general election. Confirmed contests include Gorton and Denton in February, multiple seats in June, Makerfield, Aberdeen South, Arbroath and Broughty Ferry, Runcorn and Helsby, and Clacton in August, with Holborn and St Pancras scheduled for early October. These align with typical mid-parliament patterns where annual by-election counts often range from four to eight, driven by individual MP decisions rather than systemic events. Limited additional vacancies have emerged in recent months, supporting the narrow clustering around six or seven, while the low odds on higher totals reflect the absence of widespread retirements or extraordinary circumstances that would accelerate further contests before year-end.