Opinion ladies! I have read mostly in my books that week 12 marks that final week of your first trimester and the start of week 13 is the first week of your second trimester. The bump says differently though unless I was reading wrong?! The bump says week 13 marks the final week of your first trimester and the start of week 14 is the first week in your second trimester. I'm not sure I believe some of the information on the bump 100 percent of the time since it had calculated my due date a whole week early. Both my period tracker and midwife calculated my date as 12/14 not 12/8. Please someone give me the correct information?!