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How to Calculate Conception Date

on Oct 24, 2012

by Lindsey Zaldivar

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How to Calculate Conception Date

How do you find out the day you conceived? Find out how to do the math and figure it out here.

When you find out that you’re pregnant, naturally the first thing you want to know is your due date! That is completely normal, since that is the exciting day that you will get to meet your little one! However, your next question might be what day you conceived. It sounds pretty simple right? Your conception date will be the day you had sex, right? Not so fast… Remember that sperm can live in the body for up to five days, so the day you had sex is not necessarily the date you conceived. Let’s explain how to figure out the date you conceived. Claim Your 20 Free Pregnancy Tests – Click Here

Figuring out your date of conception

If you have already been to the doctor, and know your expected due date, figuring out your date of conception is quick and easy! All you need to do is start with your due date, and count back 266 days. Simple as that! If that sounds like too much work to you, there are also a ton of online conception/due date calculators that will do all the work for you. So, if you know your due date already, it is a snap to figure out your date of conception. However, if you have not seen a doctor yet, and are trying to figure out your date of conception, it might be a little bit harder to figure out. If you have already been charting your cycles for ovulation purposes, figuring out your date of conception might be a bit easier. If you know when you ovulate, you know that your egg must be fertilized within 24 hours of ovulation, so that can narrow it down quite a bit for you.

Do the math!

However, this is how to determine an estimated date of conception if you haven’t been tracking your cycles. First of all, determine the date that you started your last period, and mark it down, if you haven’t already. Then add eleven days to the date your last period started. This is the first day that it was possible for you to conceive. Now, add another ten days to the first day that conception was possible. Those ten days are the days that it is possible for you to have conceived. You will have to narrow it down within those ten days to determine what your actual date of conception was.

Remember: conception dates are just estimates

Keep in mind, that just like due dates, conception dates are usually just estimates. You can sometimes pinpoint the exact date that you conceived, but not always. At least knowing your estimated date of conception will give you a better idea of when you conceived. As always, keep in mind that even if you do know your date of conception and your due date, it is no guarantee of when your baby will arrive. Babies come whenever they decide it’s time!

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How to Calculate Conception Date, 4.5 out of 5 based on 50 ratings

Lindsey lives in Roselle, Illinois with her husband and son Harry. In between keeping up with a busy toddler, she enjoys blogging about parenting, cooking, crafting at The Accidental Wallflower.

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  • megan

    I just found out that I’m 4weeks pregnant and its been 2-3 weeks since my last ovulation, is there any way I could find out what day would I have gotten pregnant exactly?

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  • nicki1

    My due dates tge 6th october 2014 im really confused on when I conceived im 26 weeks 2 days

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  • Tammy walker

    My due date calculating from my last period is December 2,2014 an from the ultra sound December 4, 2014 which days did I concieve

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  • liyah

    Can you get a positive Home pregnancy test 8 days after unprotected sex?

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  • chelsea

    How long does it take for hCG to be present in urine?

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  • marie

    The last time I had sex with my ex was april 19. I conceived between may 1st and 6th based on my due date. My boyfriend doesnt believe its his. Is it possible the baby could by my exes

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  • smells

    hi licia i have a quick question

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  • MommyKe

    I’m 6 weeks and 4 days pregnant as of today July 23. So why don’t I just count back 6 weeks & 4 days (which would land on June 7) to determine the day I got pregnant? Wouldn’t that mean I got pregnant 6 weeks and 4 days ago (so on June 7 I got pregnant)

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  • MommyKe

    Oh and I’m due March 14, 2015

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  • Kate

    I had sex February 23rd one night stand kind of deal. I Big mistake on my behalf. I had sex after this with my current boyfriend I am 18 weeks pregnant and my due date is Christmas Day 2014. Can some one please reassure me that I didn’t get pregnant in February. What confuses me is in march I had my period like 3 times. Help

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  • Erick Velasco

    hi im due 31.12.14 when was ir most lkely i got pregnant

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  • Jessica

    My due date is December 18th 2014 im 21 weeks and my last period was march 13th 2014. When did i conceive? And how accurate is that?

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  • Jessica

    My due date is December 18th 2014 im 21 weeks and my last period was march 13th 2014. When did i conceive? And how accurate is that??

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  • bebe23

    Hi, I just recently had unprotected sex while I was on my period is it possible for me to become pregnant? Because all of a sudden it was heavy then became light and now its gone and my period is regular.

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  • Rosie

    My Due Date Is September 16 2014 I Had Sex On Dec 22nd 2013 Is My Due Date Right My Last Menstural Was Dec 7

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  • cherry white

    I have a very regular periods an an exact 28 day cycle. My last period came on tuseday 6th May I begin bleeding in the night so first thing in the morning I’m on, I had intercourse on the following Friday 16th an 17th then again on the 19th an 20th of May I was due to come on The 3rd of June but didn’t as now pregnant I went for my scan 6th August thinking I would be 13weeks an one day but they told me I’m 13weeks an 3 days with 8th Feb 2015 being my due date the thing is I slept with 2 different guys my hub was on the 19th an 20th an the other guy on the 16th an 17th but they both pulled out and now I’m very unsure on whom I conceived with an was wondering if you could help

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  • Mommy2

    Need some advise I had 2 sex partners which one I slept with on May 10,2014 only one time and he pulled out I don’t remember when I started my period but I know it was between the 13 to the 15 of May and and ended around the 19 or the 20 th of May then I had sex with my second partner (my current bf) on the 24 of May 2014 and has been constant since then , I missed my period in June and sound out I was about 7 weeks pregnent on July 9 and I was given a due date of Feb 20,2015 and changed to feb 13,2015 and changed again on the 12 of feb 2015 I really would have like to know when I for pregnent and maybe the patential father

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  • Shell87

    I’m in the exact same boat as this! My baby was due march 13 2014 by ultrasound, he was born 10th march, I had unprotected sex may 16th but took levonelle within 10hours had heavy bleeding June 15th so went to A&E where they done pregnancy tests that were negative (urine and blood) I’ve spoke to my doctor and he’s said there is no way I conceived in May it was between 14th-21st of june.. If it was may it would mean I gave birth at 44+4 weeks. Hope this helps! It’s drove me crazy!

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  • lia

    If I had sex Feb 13 then had a period Feb 23 and sex with my bf March 7 when did I get pregnant before or after my period and my due date is Nov 30.

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  • Armani Sharpe

    If you had sex on February the 19th and then had your period March 2nd and had sex with another partner threw March 8 to April 1st then find out your pregnant April 16 and your first ultra sound was may 7 and you was 9 weeks 5 days how to know when your pregnancy started and who is the father???? And my due date is December 7th 2014

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  • howard

    Am 28 weeks pregnant and my last lamp was 2-16-2014 when did I get pregnant and how long do sperm Live in side you

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  • tuh1

    I had my baby November 11 n slept with my childs father February 19th….

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  • Shell

    You count back 4 weeks and 4 days! Last menstrual period June 7th conception around 21st June give or take a few days!

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  • Shell

    Beginning of July

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  • Shell

    If you took plan b within the first 12hrs it has a 95% chance of working

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  • She’ll

    She could go to 42 weeks… Her due date I’m presuming was 9th feb so it is possible she’s overdue they wouldn’t allow her to go over more than 2 weeks

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  • Shell

    Conception would be around June 7th

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  • Gabbsx316

    im not sure who the father of my baby is…

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  • Gabbsx316

    Can anyone help me? Im 5 months pregnant my due date is December 27th 2014. Im not sure who the father of my unborn child is. My LMP was on 3/22/2014. I had intercourse 3/27/2014 with the person im hoping is NOT the father of my baby. I had sex with my boyfriend (that im hoping is the father of my child) 4/1/2014 – 4/6/2014.. I took a prenatal paternity test by DDC (DNA Diagnostic Center) on 6/18/2014. I tested the father that im hoping is not the father of my baby & the results came back that he is EXCLUDED.. Im relieved but still kinda scared… I pray every night that he is not the father of my child because I do not plan to be with him for the rest of my life… Can anyone help me. Please do not post anything ugly. We all make mistakes …

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  • Morganne Taylor

    I’m in a dilema and I need help. My boyfriend & I broke up & I had unprotected sex Feb.7-10 with someone else. My boyfriend and I got back together on the 11th. My due date is November 16 according to ultrasound. Who’s the father? Please help. My doctors tell me there’s no way my baby is my ex’s but I need more closure because I am really stressing,

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  • cherylonie

    my last period was march28,2014 i had sex on April5,2014. I want to know when did I get pregnant?

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  • Sarah

    My due date is April 17, 2015 when did i conceive

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