Gun salutes will be fired to mark the 64th anniversary of the Queen's accession to the throne.
Accession Day on February 6 commemorates the start of the Queen's reign, which began on the death of her father, King George VI.
As she does most years, the Queen is likely to be reflecting on the anniversary of her father's death in private at Sandringham, where she has been staying for her annual winter break.
George VI died in his sleep at Sandringham House on the royal estate in Norfolk on February 6 1952 after suffering from lung cancer.
Princess Elizabeth, who was just 25, was thousands of miles away in Kenya on a Commonwealth tour with the Duke of Edinburgh when she learned of his death. She returned home a queen.
A 41-gun salute will be fired by the King's Troop Royal Horse Artillery in London's Green Park and a 62-gun salute by the Honourable Artillery Company at the Tower of London.
Soldiers from The King's Troop, the ceremonial saluting battery of the Household Division, will take up positions in Hyde Park later.
Before their arrival, the Band of the Royal Artillery will play a selection of celebratory music close to the firing position.
Seventy-one horses will pull six First World War-era 13-pounder field guns into position in the park and a 41-gun Royal Salute will be fired at midday.
At 1pm at the Tower of London, The Honourable Artillery Company will fire a 62-round Royal Salute from Gun Wharf - with an extra 21 volleys for the citizens of the City of London to show their loyalty to the monarch.
Later in the year the Queen has a milestone birthday in April when she will turn 90, and a weekend of national events are planned to coincide with her official birthday celebrations in June.