When do you think 3rd trimester begin?

Question

I see a lot of people saying 3rd trimester begin at 28 weeks but some are saying 27 weeks .... there are 13 weeks in a trimester 13 + 13 = 26 which means 26 weeks is the last week of second trimester meaning 27 weeks is the beginning of 3rd trimester. 
I honestly been going off my doctor & glow with where i am in trimester also this charts below 
I’m 26 weeks tomorrow and my doctor told me next week is the beginning of my 3rd and final trimester also being 7 months

Answer

A book I’m reading called “your pregnancy and child birth month by month” written by the American college of gynecologists says third trimester begins at 27 weeks. The math works out just like you did it. 27+13 equals 40 and that’s how long we’re pregnant for so that makes the most sense.

Answer

It’s 27 weeks, what I found funny is when I checked this app since turning 26 weeks today it’s said congratulation you made it to 3rd trimester. I’m like this app just gave me wrong info. Lol

Answer

I say 27 weeks. Maybe it’s 3 days early but there’s a good chance my baby will come 2-3 weeks early based on previous babies so I’m fine with that.

Answer

This is the one I follow so technically at like 27+3.5 is the start of 3rd trimester but I’m saying 28.

When do you think 3rd trimester begin?

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