The British supermodel greeted the landmark birthday in typically rocking style by posing as a bunny girl for Playboy magazine in black stilettos and rabbit ears.
She riled a few feminists but it was hard to deny that while the years may be rushing by, she's still got it.
Moss has recently fronted campaigns by Versace and Rimmel and although catwalk appearances are now rare, barely a month goes by where her image is not on the front pages.
The Londoner is the fourth highest-paid model in the world, according to Forbes, earning $5.7 million, between June 2012 and June 2013.
Behind the cameras, Moss has a busy few months coming up as she makes her debut as contributing fashion editor at British Vogue, and in April launches an eagerly anticipated new collaboration with high-street fashion powerhouse Topshop.
Moss is everywhere, but her reticence to speak to the media means she remains something of a mystery - the result of a strategy recommended by ex-boyfriend Johnny Depp.
"He told me 'never complain, never explain'," she wrote in her 2012 book, Kate: The Kate Moss Book.
"That's why I don't use Twitter and things like that. I don't want people to know what is true all the time and that's what keeps the mystery."
This unknown element has only fuelled the curiosity, along with the rock'n'roll lifestyle - Moss used to date tortured Libertines frontman Pete Doherty, and is currently married to Jamie Hince, guitarist for The Kills.
She is rumoured to be planning an epic birthday party on Necker Island, tycoon Richard Branson's private retreat in the Caribbean - possibly with a Playboy theme.
'Inimitable style'
The glossy has dedicated 17 pages to Moss' 40th birthday, and Ormerod says her readers have always identified with her fun-loving side.
"Her legendary parties and glamorous costumes make her more than just another model," she told AFP.
"Plus Kate's style - which has remained constant with a host of signatures, rather than following every single trend - is inimitable."
Moss's birthday has been marked by a London exhibition of pictures taken from photographs throughout her career, and a documentary on French television, "Looking for Kate".
Moss is not just a clothes horse but also a muse, inspiring the painter Lucian Freud, sculptor Marc Quinn and designer John Galliano, who she famously supported through his fall-out with Dior.
The daughter of a barmaid and a travel agent from Croydon, a famously drab suburb of south London, Moss has always lived on the edge of scandal.
Early in her career, after she was spotted aged 14 at New York's JFK airport, the pale faced young model became the face of 1990s "heroin chic", a fashion trend blamed for glamorising drugs and anorexia.
Moss was accused again of being a bad role model in 2009 when she quipped that "nothing tastes as good as skinny feels".
In 2005, she lost several major contracts after a video emerged apparently showing Moss taking cocaine, although she soon won them back.
Every few years, a model comes along who is touted as the new Kate Moss, currently Cara Delevingne.
"But there will never be a new Kate, in the same way there will never be another Coco Chanel or Marilyn Monroe - she's a one-off," says Ormerod.
At least, perhaps, until Moss' 11-year-old daughter Lila Grace or another member of her family comes of age - her half-sister Lottie, 16, recently signed up to the same modelling agency, Storm.
AFP-Relaxnews