This year is an eventful one for the monarch as in the summer she will mark the 60th anniversary of her coronation, staged at Westminster Abbey on June 2 1953.
Her third great grandchild and a future sovereign is expected to be born in mid-July to the Duke and Duchess of Cambridge.
A Buckingham Palace spokeswoman said the Queen would celebrate her birthday on Sunday privately.
It is thought the Queen and Duke of Edinburgh are staying at Windsor Castle, said to be their favourite home.
The monarch's milestone will be marked across the UK with traditional gun salutes fired in celebration.
But as the birthday falls on a Sunday this year the military tributes will be held on Monday.
In London the King's Troop Royal Horse Artillery, the ceremonial saluting battery of the Household Division, will fire a 41-gun royal salute from Green Park at midday.
The military unit provided the gun carriage that bore the coffin of Baroness Thatcher in the ceremonial procession to St Paul's cathedral on Wednesday.
The gun and the horses that were part of the funeral cortege will take part in the gun salute.
Before the King's Troop arrive in Green Park, the Band of the Royal Artillery will play a selection of celebratory music close to the firing position.
Princess Elizabeth Alexandra Mary was born at 2.40am on April 21 1926 - the first child of the Duke and Duchess of York - at 17 Bruton Street, the Mayfair home of her mother's parents, the Earl and Countess of Strathmore.
She is the great-great-grandchild of Queen Victoria, the previous female sovereign.
Queen Elizabeth II, who is Head of State, the Armed Forces, the Commonwealth and the Church of England, has been married to the Duke of Edinburgh for more than 65 years, has four children and is grandmother to eight grandchildren.
She carried out 325 UK engagements in 2011.
The monarch has two birthdays - her actual birthday celebrated on April 21 and her official one in June, which is marked with the Trooping the Colour parade.
