The newest way to count months for pregnancy is every 4 weeks is a month. This is the new standard so the break down posted above is accurate. This means you are pregnant for 40 weeks/10 months (however remember they use from the first day of your last period, so you really are only pregnant for 38 seeks, so this is where the 9 month theory comes from--this is the older counting method of duration of pregnancy- which is why everyone says pregnant for 9 months)
However, it doesn't really matter how many months you are as in pregnancy you normally go by weeks. If you are wanting to be able to tell people you are in your third trimester then its your decision to tell them you are at 27-28 weeks. Either way its only a few days until anyone you most deffently are in your third trimester.
It's just that, you go by weeks. Not months. Because depending on when you start counting your "month" will be different than another's because if you got pregnant in February and them in august it'll be a different amounts to of months but same amount of weeks. I personally go by weeks and by doing so it would be considered a pregnancy of 10 months. 25-28 is "month 7" to me. 29-32 is "month 8" and so on till 40wks.
Everyone counts different. People will say a month of pregnancy is every 4 weeks which doesn't make sense because 40 weeks is technically 10 months not 9 months. If you counted by every four weeks than s full term pregnancy would be at 36 weeks.... So in pregnancy term months 3,6,8, and 9 have an extra week added there for which would make you 7 months at 27 weeks.
People will disagree but this is how my doctor taught me and makes much more sense than every four weeks
First trimester:
Month one: weeks 1-4
Month two: weeks 5-8
Month three: weeks 9-13
Second trimester:
Month four: weeks 14-17
Month five: weeks 18-21
Month six: weeks 22-26
Third trimester:
Month seven: weeks 27-30
Month eight: weeks 31-35
Month nine: weeks 36-40
No at 28 weeks is the start of the 7 month for most of us up here. But it Depends on what your doctor goes by...but ive never seen 25 weeks as 7 months