When to tell ppl at work?

I'm almost nine weeks but not really showing at all. When is a good time to start telling people at work? I want to have my work plan figured out by the time I announce it so I can discuss my maternity/post-birth plan with my supervisor. I'll prob have to tell everyone at the same time tho because it's a tight knit group and trying to make anyone keep a secret is impossible. 😊 Any advice?