wtf trimester lol

Katlyne • Single Momma of 2💜 Annabella Desire’e Lee 👶🏻👑👸🏻🌈 12.04.17, 8lbs 5.5ozs. Edward Alekzander 👶🏻👑🤴🏻♥️ 02.06.19, 8lbs 12ozs.
What week do you ladies think the second trimester begins? 
When I first got pregnant with my angel I thought it was 12 but I lost my baby so I didn't think anymore of it. 
Now I'm 13 weeks as of today and I've looked it up and the internet says 13-27 weeks is the second trimester. But all my pregnancy apps still say 1st trimesters. Soooo what week do y'all see as the start of second trimester??