End of first trimester

mariajay06

When does the first trimester actually end? I've read so many conflicting things. Some say end of week 12 and some say end of week 13.

lovesclimbing

I consider it around 13.5 weeks. Technically, a pregnancy is considered 280 days. If you divide that by 3 (trimesters) and then divide that by 7 (days in a week), you get 13.33. So 13 1/3 weeks.