Music streaming is likely to play a bigger role in the Christmas number one race than ever before.
Last Christmas, streaming counted towards around 25% of the total - but in the final few months of 2015, it has accounted for around half.
Audio streams started contributing towards the singles chart in summer 2014, with 100 track streams equating to one sale.
The Christmas number one will be announced by 1pm on Christmas Day.
Sales and streams will be counted up to midnight on Christmas Eve, with the result being announced less than 13 hours later.
It will be only the fourth time the number one has been declared on Christmas Day itself, following a December 25 announcement in 1994, 2005 and 2011.
It is likely the X-Factor winner will be in the running for the Christmas number one spot.
Louisa Johnson, 17, will compete against Che Chesterman and duo Reggie 'N' Bollie in this weekend's final of the show.
But this year's final is earlier than usual, ending on December 13, which could mean the strongest sales come before the race for number one kicks off on December 18.
Other contenders include a campaign single by The Lewisham & Greenwich NHS Choir, plus tracks by Kylie Minogue, Dame Shirley Bassey, The Darkness, Shakin' Stevens, Carly Rae Jepsen and the Military Wives.
The Star Wars theme could also prove a hit after the latest movie is released on December 17.
This year's winner will be the UK's 64th official Christmas number one.
The Beatles are the all-time Christmas number one champions, having topped the charts four times with I Want To Hold Your Hand (1963), I Feel Fine (1964), Day Tripper/We Can Work It Out (1965) and Hello, Goodbye (1967).
The Spice Girls scored three successive Christmas number ones in 1996, 1997 and 1998 with 2 Become 1, Too Much and Goodbye respectively.
Queen's Bohemian Rhapsody has been Christmas number one twice, in 1975 and 1991.
The song Do They Know It's Christmas has gained the top spot three times, as it was performed by Band Aid (1984), Band Aid II (1989) and Band Aid 20 (2004).
BBC Radio 1 will count down the festive chart between 10am and 1pm.