The Duchess of Cambridge will reach the milestone age later this month but has decided not to have a big party, because of the Covid-19 pandemic.
A source told The Mail On Sunday newspaper: "There are likely to be low-key celebrations for the Duchess.
She didn’t want anything flashy anyway – that’s not exactly her thing – but particularly given the current climate anything is likely to be scaled down."
The celebrations will be small and will include only close friends and family.
This comes after Catherine, her husband Prince William, 39, and their children Princes George and Louis, eight and three, and six-year-old Princess Charlotte, spent Christmas with her family at Anmer Hall in Norfolk.
Their decision to remain in Norfolk came after it was revealed that Queen Elizabeth, 95, had decided to remain at Windsor Castle for the festive period, rather than make her traditional trip to her Sandringham Estate.
The Queen had intended to follow tradition by spending Christmas at her royal residence in Norfolk, but she cancelled those plans amid rising levels of the Omicron variant in the UK.
The decision "reflects a precautionary approach", according to Buckingham Palace aides, who confirmed that it was a personal decision taken by the monarch.