Knowing how to date a pregnancy is important because it impacts decisions made in the last month of pregnancy.
How to Date a Pregnancy
Pregnancy dating is based on the assumption that every woman has a 28 day cycle and that ovulation occurs on day 14.
Care providers also assume that every woman has a two week luteal phase.
Luteal Phase = A luteal phase is the period of time from ovulation until you get your period.
To calculate a due date simply add 38 weeks to the date you ovulated/conceived and that is your estimated due date.
Super Sperm
However, the date of conception/ovulation isn’t always the day you had sex.
FACT: Did you know that sperm can live in your body for 5-6 days post intercourse? This means that the date of conception (which is when you ovulate) could be up to 6 days after you did the deed.
I got pregnant two times by having unprotected sex SIX days before I ovulated. TWO TIMES! The first resulted in a miscarriage but the second resulted in my beautiful daughter, Mercy.
In order to know the exact date of conception it’s important to know the exact date of ovulation instead of the exact day of intercourse.
Benefits of Using the Fertility Awareness Method
Since I chart and practice the Fertility Awareness Method I always know when I ovulate. Always. Even if I weren’t charting, I would know.
After years of paying attention to the signs of my fertility I cannot not know what is going on.
Because of this, when I get pregnant I always know how to date a pregnancy and what my true EDD (estimated due date) is. When I go in for an ultrasound and the baby isn’t measuring up to my dates I know something is very wrong.
For my most recent pregnancy, when I went in for an ultrasound and their measurements were spot on to mine I knew all was well.
I’m Not Calling It a Lie
Yes, some women have these regular text book cycles, but a lot of women do not. I am one of those women who absolutely, positively does not have a regular cycle. My cycles even differ from each other, month to month.
Because most care providers want a LMP (last menstrual period) date on the first appointment, instead of giving them my true LMP I subtract two weeks from my ovulation date so that they will calculate the same EDD as I do.
For example, during my second pregnancy my LMP was 2/29/2012 which made my EDD 12/5/2012 which was wrong, wrong, wrong.
Based on ovulation a more accurate due date was 12/13/2012.
If I went by my true LMP date I would be more than a week off!
Accurate EDD = Less Inductions
For all those mamas who have their babies after their due dates we all know how valuable that extra week of time is in order to avoid an induction.
(Update: I gave birth to my daughter on 12/12/12 and I guarantee you if I had the estimated due date of 12/5/12 induction would have been a topic of conversation between my care provider and I! Because I used my TRUE estimated due date we never even talked about it. Information is empowering!)
A Sense of Control
To know my true EDD and not have someone tell me also gives me a sense of control and empowerment. I like to inform doctors of my body, and not them inform me of it instead.
If this article was a little hard to understand I recommend reading the book Taking Charge of Your Fertility so that you can understand what in the world I’m talking about. 🙂 It will change your life!
Educate Yourself
The moral of this story is to educate yourself. Know your body, your cycles and give yourself the upper hand by knowing your true estimated due date (EDD) before you see your care provider. Knowing how to date a pregnancy correctly is a game changer.
Leave a Comment
Leave me a comment and let me know your story of EDD’s. What do you know now, that you didn’t know before?
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sarahkeith says
I was glad that I had been charting when we conceived because I found that I generally ovulated around cycle day 21, not cycle day 14! My calculated due date would also be a week “early”, if I didn’t know that. I loved the experience of learning to recognize fertility signs.
Lindsey Morrow says
I love hearing that other women do this too. It’s so empowering to figure out this information on our own!
Leslee says
I usually ovulate much later than “normal” around day 18-20, but only have an 11 day luteal phase, so my cycles tend to be around “normal” length. If I didn’t chart, I’d have no clue! That being said, I had to correct my LMP dates because we did IVF to conceive which made my dates off by about three weeks. I would flat out correct them and say that while my LMP was at the beginning of October, the date of conception was at the beginning of November so they needed to correct them in their system so that the baby wasn’t measuring off or would be considered overdue when she was technically still three weeks from fully baked. What a hassle, though!
Lindsey Morrow says
YES! It’s quite a hassle to explain. Especially if you have to do it over and over again. That’s why I give my fake dates. 😉
Amber Kearney says
I kept telling my doctor her date was wrong. I knew when I had conceived but they went by my lmp. Wouldn’t you know it- I was induced. Next time around I will do this. Thanks for the tip.
Fatima says
How to get a girl?
Meagan says
Haha! I love this. I love the TCOYF! very empowering to read and learn. I am 8/9wks pregnant. But the normal due date method has me at 10/11wks. WHY DO DRs include my 6days bleeding as a pregnancy week? And the week after in which NO ovulation occurred?! I quit charting 7months ago for hubby n I to have an unplanned/surprise pregnancy. But one can’t ignore 8yrs of using fertility awareness! I know roughly when I ovulated. So I’m scheduled for a 1st appointment in a week and I want to make this point. But in your experience it’s better to say your ovulation date as your 1st day of LMP ?
Lindsey Morrow says
I would adjust your LMP to give you the due date that most accurately reflects your pregnancy. Does that make sense?
Meagan says
Yes It Does! Thank you for responding!
Yeddy says
Hi, I read your post hoping that I’d find an answer for my situation… I had my implanon removed on 6 Aug & sleep with my husband till about a week later. According to the doctor, I am now 21 weeks pregnant as of today. I wanted to find out if this is accurate & to learn to calculate the right date myself. Any ideas?
Lindsey Morrow says
It’s hard for me to know without knowing *exactly* when you ovulated. For a good guess, add 38 weeks to the date you had sex OR 40 weeks from the first day of your last menstrual period. That should give you some good guesses for your due date. Hope that helps!
Richa says
even i had estimated my due date but that was not with the calculator i mean i didnt know if we could time the birth date so well. thanks for sharing great content.
Annalisa says
They would have started talking induction before you even got to 41 weeks? :O Based on the reading I’ve been doing, a baby isn’t even *late* until 42 weeks. (That may be due to the fact that LMP isn’t 100% accurate.) I was born at 41+5 and they were planning on inducing the next day, but there were signs I was no longer in a good place (but my mother at least didn’t have to deal with meconium in my first diaper…just inside of her).
Where I am currently going, I told them I was 17 weeks (before I had even seen the doctor), and they wrote “16” on my chart; it felt nice that they were going to give me that extra week and not rush baby. Based on my LMP, I was due August 3rd, but the first trimester ultrasound said August 7th.
My next appointment isn’t until 28 weeks (based on the original ultrasound), and at that point the doc and I will need to sit down and have a nice chat about philosophy. (This is one of only two providers covered through my husband’s work, but I have a few deal breakers which would make us opt for a private hospital.)
Monica says
I wish I have seen this before. I calculated my due date based on my ovulation and is giving me agoust 14. The doctor’s due date is agoust 11 and even I am not even late yet, they already started the conversation of induction and I am freaking out. I have my check up the 11th when they will set an induction date. I am prepared to delayed as much as possible but I really wish I had this extra 3 days. Every morning I wake up thinking one more day with no contractions, I am going crazy.
Lindsey says
Check out this post for tips on working with your care providers. It sounds like it may come in handy! https://www.motherrisingbirth.com/2016/02/brain-acronym.html
Olivia Layne says
Hi 🙂 Doing ALL the research on being pregnant! Just found out we’re expecting our first 2 days ago. My LMP was 9/4, but I didn’t ovulate until around 9/17-9/23. For some reason I didn’t track super well that week. Oops! So according to my LMP I’m 5 weeks today, but according to ovulation I’m somewhere around 2/3 weeks. But I didn’t even know you could find out that early. I missed my period and 2 tests have come back positive so I know I’m pregnant. Literally so confused. Help!
MAddie says
I did the same thing! Since I use NFP I gave my midwife the “corrected” date of my last period, since I knew I often ovulated on days 18-21. Measurements were always spot on and my labor started the day after my due date! Knowing your own fertility signs and tracking is so so helpful!
Lindsey says
We are kindred spirits! 🙂
VaL says
I’m so confused to when I ovulate. I want to say I don’t ovulate as much. I am doing the ovulation kit every morning when I wake up to see if I’m fertile or not. So hard to determine if it’s accurate. The all’s aren’t much help because when I tear myself (ovulation kit) it doesn’t say I’m ovulating but my all days I am??:/
Any recommendations?
Lindsey says
I would read the book Taking Charge of Your Fertility. It changed my life. 🙂