When is the first trimester over?

Question

I have read conflicting answers. Some say the last day of week 12. Some say the last day of week 13.

Answer

I consider 14 weeks the start of second trimester.  But it doesn't really matter much to me I guess🤷🏼‍♀️

Answer

I heard second trimester starts at 14 weeks 🤷🏼‍♀️

Answer

Second trimester starts at 13 weeks.