When to tell my boss I am pregnant?

Natalie • Married, mommy to a baby 🎀 & baby 🎀 #2 due July2020

I had my 1st baby at 34 in Oct 2018 and I am currently pregnant with #2 due July 2020. I don't know why I am nervous to tell them this time, but I am. When should I tell my boss & HR and when do you think it is too late?