when does the 2nd tri start?

13 or 14 weeks either or.

DEFF BOOKS AND SITS SAY DEFF THINGS. Some say 12w some say 13w6d I always thought it was 12w 6ds

at 12 weeks I have always counted it the 2nd trimester

Make a pregnancy ticker

13 and a half weeks to be right but 13 is fine. cuz 13 weeks later is the 3rd trimester. 14 weeks later your due

Quoting housefullofkidz:

Cute chart :O)

My doctor says its 13.5 weeks. Hope that helps....so many people have a different opinion. I have heard 12 weeks, 13 weeks. 13.5 weeks...and 14 weeks. But I go by what my doctor says and like I said is 13.5! Good Luck and Congrats! 

The beginning of your 14th week marks the beginning of your second trimester. The third trimester starts the beginning of the 28th week.