I am going by LMP weeks completed. So I am due April 4, and that makes me 6 weeks 5 days by those dates (more or less), but I am 33 days pregnant. Because I have a shorter cycle, I get a few days 'credit' with the LMP. So I put my ticker on 6 weeks, because it is a 40 week ticker rather than a 38 week.
By Naegel's rule (the dates way of dating a pregnancy) you take the first day of the last menstrual period (in my case July 1). Go back three months, and add 7 days = April 7. But because my cycles are 24-25 days, I subtracted 3 days (because it's not a 28 day cycle) and got Apr 4. Some people don't use an adjusted Naegel's rule where you subtract or add days depending on their variance from a 28 day cycle, but I find it logically the most sound, and that's what I use in my cycle.
Sorry if this post is annoying, I just wanted to explain how I got to where I am. I also have a book that has a journal for everyday of pregnancy. I plotted out all 266 days of a 'typical' gestation from my date of ovulation, counting the day after as day 1, and got April 3 as my due date, so I am feeling like my dates are pretty accurate. Now when the baby actually comes is another matter altogether!!!!