With the birthday bash expected to be a smaller than usual affair, Harry has ordered a cake from local baker Posies & Sugar for Meghan, according to The Mirror.
Meanwhile, guests will be treated to locally sourced wine, grazing tables and food from nearby eateries.
Meghan is said to have invited her friends to attend, with names like Serena Williams and Amal Clooney among those reportedly on the guest list.
Last year, Meghan celebrated her 39th birthday quietly at home amid the COVID-19 pandemic.
The restrictions on gatherings have recently been lifted in California however, allowing Meghan to celebrate this year with friends and family.
In contrast, Meghan enjoyed a lavish baby shower in 2019, and her 40th birthday will be the first time she will be celebrating a milestone as a mother-of-two.
It's been almost two months since Meghan and Harry welcomed their daughter Lilibet Diana Mountbatten-Windsor into the world, making their two-year-old son Archie a big brother.
The couple have kept their children out of the limelight, but are reportedly planning a private christening for Lilibet with only a handful of their closest friends expected to attend.
“Meghan wants the ceremony to be super small, and will only include a handful of celebrity friends, along with her mum, Doria,” a source revealed to New Idea recently.