Vote for the Mayor and London Assembly on Thursday 6 May 2021

Counting the votes

Counting the votes

The day after polling day, Londoners’ votes will start to be counted.

The counting will take place in three centres across London: Alexandra Palace, ExCel and Olympia. 

Owing to the scale and complexity of the elections in London, votes are counted electronically – called e-counting. Under the direction of the Greater London Returning Officer and each Constituency Returning Officer, the e-counting software calculates the results for the three contests. 

These calculations are then checked by each Constituency Returning Officer and the Greater London Returning Officer. 

The Greater London Returning Officer announces the new Mayor and the 11 London-wide Assembly Members from City Hall.The 14 Constituency London Assembly Members are announced by the relevant Constituency Returning Officers. This takes place in the count centres.

How are Mayoral results calculated?

The Mayor of London is elected by the ‘supplementary vote system’.

Each voter has a first and second choice vote. If a candidate receives more than half of all the first-choice votes they are elected. If this does not happen, the two candidates with the most first-choice votes go through to a second round. All other candidates are eliminated.

The second-choice votes of everyone whose first choice has been eliminated are then counted. Any votes for the remaining two candidates are added to their first-round totals.The candidate with the highest combined total of first and second choice votes wins.

How are Constituency London Assembly Member results calculated?

The 14 Constituency London Assembly Members are elected using the ‘first past the post system’.

This means the candidate in each constituency with the most votes is elected as a Constituency London Assembly Member.

How are London-wide Assembly Member results calculated?

The 11 London-wide Assembly Members are elected using a form of ‘proportional representation’: this system is used to ensure the overall Assembly reflects how London voted.

This means that the London-wide Assembly seats cannot be allocated until the constituency results have been announced.

The 11 seats are allocated using a mathematical formula – the ‘Modified d’Hondt Formula’. 

The formula uses the votes cast in the London-wide Assembly Member contest and takes account of the number of Constituency London Assembly Member seats that each political party has already won.

11 rounds of calculations then take place to fill the 11 vacant Assembly Member seats, with the party or independent candidate with the highest result at each round being allocated the seat. 

Seats won by parties are allocated to party candidates in the order they appeared on the relevant party’s list of candidates.

Find out more about the London Assembly.