Third Trimester???

Cheyenne
26 weeks today!!!! I'm confused about what stage things are at. I thought I wasn't in the third trimester until 27 weeks but I woke up this morning to <a href="https://play.google.com/store/apps/details?id=com.glow.android.nurture">nurture</a> saying "26 Weeks, congrats on making it to your Third Trimester of pregnancy!" How do all of you track what point your at?