West Bengal: Can SIR Redraw the 2026 Election Map?

The SIR exercise has generated intense debate in West Bengal. Between the 2021 assembly elections and the upcoming 2026 contest, over 5.16 million registered voters have been removed from the state's voter lists under a Special Intensive Revision, or SIR, exercise. That is a 7% decline across the entire electorate. 

Do the deletions have the potential to fundamentally alter who wins and who loses in Bengal's most consequential election in years where the ruling Trinamool Congress is facing a 15-year anti-incumbency with the BJP pushing the pedal? 

Source: Author's calculation from ECI Data

The distribution of deletions is not uniform. The Presidency division, which covers Kolkata and its surrounding districts including Howrah, Nadia, North and South 24 Parganas, has been hit the hardest. It shed nearly 2.8 million voters, about 10.5% of its 2021 electorate. Within the division, Kolkata itself saw a 26.4% deletion rate, meaning roughly one in four names on the city's rolls has been struck off. Howrah and North 24 Parganas followed with deletion rates of 9.8% and 11%, respectively.

Malda is Muslim-majority administrative zone lost close to 980,000 voters (-8.2%), and Bardhaman shed 970,000 (-7.1%), broadly in line with the state average. Jalpaiguri which is a BJP stronghold in the hills, saw a smaller but still significant loss of 420,000 (-6.1%).

And then there is Medinipur —the political base of Suvendu Adhikari, BJP’s chief ministerial face—the one division that is an outlier: it gained 18,087 voters. Every other division contracted. Medinipur did not. 

The Partisan Question

Raw voter deletions mean little unless you understand whose votes are being removed. This is where the political stakes crystallise sharply.

In West Bengal's 112 assembly seats where Muslims constitute 25-30% or more of the electorate, the Trinamool Congress has been overwhelmingly dominant. In 2021, TMC won 106 of these 112 seats, often by margins exceeding 15%. These constituencies are the bedrock of Mamata Banerjee's electoral coalition. Any structural erosion of the Muslim voter base, whether through outmigration, death removals, or illegal immigrant deletions, directly threatens TMC's position.

The analysis suggests that if even a significant fraction of the deleted voters are drawn from TMC's support base, 20 of these 112 seats become vulnerable for the party. 

The Battleground
Nowhere are the numbers more dramatic than in the Presidency zone's 108 assembly constituencies. TMC has held 93 to 95 seats here consistently across three elections since 2011, with vote shares running 3 points above the state average.

In the 2021 election, TMC swept all 27 Kolkata and Howrah seats. BJP had pockets of competitiveness in Nadia (Matua belt), but elsewhere in the zone it was largely a bystander.

In the Presidency zone, the average deletions per seat are around 26,000 votes, whereas the average margin of TMC in 2021 was 35,000. Here as well, scenario projections built on the assumption that all deletions are TMC voters put 33 seats in the vulnerable category for Mamata’s party. 

The reality will be more complex — deletions will include deceased voters, duplicates, and genuine relocations. 

The Number Conundrum
What is certain is this: 5.1 million deleted voters is not a clerical correction. Trinamool Congress enters 2026 with structural vulnerabilities it did not face in 2021. The 2026 West Bengal election will be decided not just by who campaigns better, but by who is still on the rolls when polling day arrives.