Here is a look at the royal baby by numbers:
2 - Baby Cambridge has two homes - Kensington Palace's 20-room Apartment 1A in London and 10-bedroom country residence Anmer Hall in Norfolk.
3 - The new royal baby will be the Duke and Duchess of Cambridge's third child - a younger sibling to Prince George and Princess Charlotte.
5 - William and Kate's baby will be born fifth in line to the throne. The baby is also a 5 x great-grandchild of Queen Victoria.
6 - The baby is the Queen's sixth great-grandchild. The baby will bump Prince Harry down to sixth in line.
7 - The Cambridges celebrate their seventh wedding anniversary on April 29.
9 - Weeks of age Princess Charlotte was when she was christened. George was 13 weeks old at his christening.
15 - Years William and Kate have been together.
35 - Number of months between Charlotte and the new baby. Kate and William will have three children aged four and under.
36 - Kate is 36. William turns 36 in June this year.
41 - Royal births are celebrated with a 41-gun salute.
£7,500 - Cost of a one night stay and delivery package at the private Lindo Wing including a suite of two rooms, but excluding consultants' fees.
£9,450 - Cost per year for Willcocks Nursery School, which Charlotte attends.
1.2 million - Followers of the Cambridges' official Twitter account @KensingtonRoyal.
£4.5 million - Cost to the taxpayer of refurbishing William and Kate's Kensington Palace apartment in 2012.
£42.8 million - The amount the Queen received from the taxpayer via the Sovereign Grant in 2016-2017 - 65p for each person in the country.