July 28, 2023

Conception Calculator: Calculate When Did You Conceive

Realizing that you are pregnant is an emotional moment. It is intense to think of the changes your body will go through, the responsibility you now have for another life, and how you will care for your baby. All of these emotions are heightened if you have questions about when your child was conceived. If you do have questions, there is a simple way to set your mind at ease: you can consult a conception calculator.


Conception Calculator will estimate probable conception dates
from Birth, LMP and Due dates.

These are probable conception dates based on an average cycle of 28 days.

To use the calculator:
1 Choose either the
Due Date / Birth Date or
the First Day of Last Menstrual Period,

2 Enter the date, and
3 Click the 'Calculate' button.
Results:  

First Day of Last Menstrual Period: 

Probable Date of Ovulation:  ?

Possible Dates of Conception:  ?

Due Date:   (40 weeks)

What is a conception calculator?

It is a calculator that allows you to enter your due date/baby’s birth date or the first day of your last period. The calculator takes that date and gives you a window of about eight days when you might have conceived. This is an easy and private way to answer questions you might have about your conception date and who your baby’s father might be.

Why is the conception calculator accurate?

Your menstrual cycle typically includes five days each month when you have a chance of conception. Those are the days you ovulate. For the most part, that is around twelve to sixteen days before you have your period. You must also factor in that a man’s sperm can remain viable for three to five days inside you. That means you still might become pregnant if you have sex within that time before you ovulate.

Obviously, if you get your period between the date on which you have sex with a man and the date you conceive, then he can’t be your baby’s father. Keep all those facts in mind when you use the conception calculator to determine who might be the father of your baby. It also helps you project forward and determine the possible due date of your baby.

Let’s look at an example of how the conception calculator works:

Suppose you choose to enter the first day of your last period. Let’s say that day was March 20, 2016. If you enter that date, you will find out that the most likely date of ovulation was April 3, 2016. That is fifteen days after the first date of your period. An ovulation date of April 3rd leaves a window of conception from March 30th to April 7th. Projecting forward 40 weeks, that gives you a due date of December 25, 2016. A Christmas baby! With that information, you know that your baby’s father could be any man you had sex with between March 30th and April 7th. This may allow you to eliminate the possibility that any man you did not have sex with during that period is your baby’s father.

The conception calculator is a great tool for you to use. Naturally, you should also be consulting your gynecologist with any questions you have about your conception date and your baby’s paternity. If, after using the conception calculator and consulting your doctor, you still have questions, you will want to have a paternity test done when the time is right. That will put any remaining doubts to rest.

Don’t let any sense of embarrassment prevent you from talking to your doctor. Your doctor is professional and bound by doctor/patient confidentially. They also have the know-how and the tools to help you be certain about your baby’s paternity. Use the conception calculator and consult your doctor so you get your questions answered and gain the certainty you need.

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24 thoughts on “Conception Calculator: Calculate When Did You Conceive

  1. I had my period from 4th to 8th february,my cycle is 25 days,I had sex with guy #1 on 10th feb and i had sex with guy #2 on 16th and 18th,still woundering who is the father of my child

    1. If i had to guess i would say guy #2 because you would’ve been ovulating around that timeframe. Did you ever get a test to pinpoint who the biological father is?

  2. Hi please someone help me know who my baby’s daddy is. I had sex with 2 different guys on dates 16th and 12th before my expected periods and they both ejaculated inside me. I also think I ovulated late on 12th day before my expected periods. Who could be the father please.

  3. Hi my doctor said I conceived October 10th I’m due June 30th is it possible for the father to be somebody I had sex with at the end of September?

  4. Hi I had my last period on the 30 of march 2018 and had sex with two different guys first guy was on the 11 of April we used protection but it breaks and the second guy was on the 17 of april we had unprotected sex severally that day.I think am pregnant because my breast sore and I miss my period please I want to know which one of them is my baby’s father.

  5. If my lmp is Jan 1 2018 and was having sex with my partner from then on and stop and had sex one time with another dude Jan 22, 2018 would my partner be the baby father?

  6. that is for a woman with 28days but its different if your cycle is short or long than that

  7. my last period was on April 11, lasted only 3 days. I had sex with a guy 1 on April 7 and Guy 2 on April 9. and Had sex again with guy 2 on May 1st. I am apparently 6 weeks and 4 days pregnant now. which intercourse got me pregnant? idk how to count pregnancy days

  8. Hi . I’m trying to figure out who is the father. My lmp was november 6 , 2017 . I had intercouse with my ex november 15 and a one night stand on november 22 . questioning who my child’s father was never crossed my mind until now .

  9. I had sex and March 2nd and 3rd with my ex and see my period on March the 5th and had sex with my bf after my period and i miss my period in April and when I did a ultrasound I was 10weeks and 6 day’s pregnant .can you plz tell me who my baby father might be

    1. Hi there Robin, please click here to find out the day that you conceived so that you can easily determine who your baby father might be.

  10. Im 4 days late, my period was supposed to start Friday March 22nd. I had sex with #1 guy on Saturday night, March 9th and Sunday night, March 10th. #2 guy I had sex with March 16th, Saturday night and Sunday night, March 17th, #2 guy we had unprotected sex and the condom slipped off inside me. Pls help

  11. Me and my GF had our little bundle of joy on Mar 24th. Our conception day was July 4th of last year. Just wanna make sure if that sounds right. Thanks

  12. Hi
    My baby was born on the 2nd of November 2019
    My lMp is 27th of January
    Had sex with bf on 28th of January while was on period and sex with someone else on 17th of February
    By the conception calculator gives out 5th to 13th of February
    Still confused on who could b the father .
    Please help

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