How far along am I? How are you calculating if your cycles aren’t always exactly 28 days?

Question

Everything says something different. Does anyone know of a calculator that will tell me based on positive opk date?
Last period August 22nd. Average cycle anywhere from 28-32 days. Peak opk 9/8, still positive 9/9. Premom says my ovulation would’ve been 9/9 based on my OPKs. According to that, my first positive pregnancy test was 9 DPO. 
Some apps say I’m 4w1d, some say 4w3d, some say 5w1d. If I didn’t track ovulation I’d be 5 weeks. I’m now 17 DPO, so I’ve known I’m pregnant for about 9 days. 
I am so confused! It’s not that big of a deal but I just like to know. Some websites have a conception date due date calculator, but we BD’ed so many times idk if it’s saying when did I ovulate or when did we BD that made us pregnant? 
Just curious how y’all are calculating it in early pregnancy.

Answer

Every single doctor will calculate from your last menstrual period, not when you ovulated. They will adjust your due date around 12 weeks at your dating scan if it’s off by a lot but more often than not it stays at the date you get from your last menstrual period.

Answer

You calculate from the first day of your last menstrual cycle

Answer

https://www.babycenter.com/pregnancy-due-date-calculator 
I use this one and then change it to calculate off date of conception and put in my ovulation date for that. Just note it may be slightly off but you’ll have a general idea until your dating scan. My midwives have always considered my longer than average cycles when calculating my due date, even before my 12 week scan. Both times I’ve told her when I think I ovulated and she calculates off that for the first trimester and both times I have been correct when the dating scan actually rolls around.

Answer

As others said, you go by LMP until your dating scan between 8-12w

Answer

Just use first day of last period and then you’ll get an updated EDD based on ultrasound measurements when they think you’re around 10-12w.
Even if you try to calculate based on cycle length, or when you think you ovulated, or which time you had sex...fertilization and implantation could have happened at a variety of times.