By when is it required to inform employer about our pregnancy?

I informed my employer when I found out I was pregnant. I'm thankful they were very supportive and kept me away from heavy duty work (like carrying items) and I also excused myself from many work events that have massive crowd. My co workers also started keeping out for me and really took good care of me during the time. As a responsibility, informing employer early will also ensure they have ample time to plan for your work while you are away. I would suggest no later than 4 months.