Conception Calculator

Probable conception and due dates

When was my baby conceived ?

Date conceived


Conception Calculator

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

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

  1. Due Date / Birth Date OR
    The First Day of
    Last Menstrual Period

  2. Enter the date

  3. Click 'Calculate'


First Day of Last Menstrual Period: 

Probable Date of Ovulation: 

Possible Dates of Conception: 

Due Date: 
 (40 weeks)

Our free ovulation planner gives a timeline of your most fertile days for getting pregnant.



When was my baby conceived?

A woman is usually able to get pregnant for about 5 days each month, when ovulation occurs. On average, ovulation occurs 12 to 16 days before the menstrual period begins. Because sperm can live for 3 to 5 days in a woman's reproductive tract, it is possible to become pregnant if intercourse occurs several days before ovulation.

Q:   I ended a relationship with an previous partner and I am now with a new partner. My doctor says I am 8 weeks pregnant. This is about the time of my change of partners, who is the father?

A:   You can use the conception calculator to get an idea of around when you conceived. Based on that date you can make a guess as to who the father is, but it will only be a guess.

If you are unsure of who the baby's father is, now really is the time to sort it out. You shouldn't be embarrased to discuss this with your doctor. I am sure your doctor has seen and heard it all, so don't be worried. Visit the calculator and see what date you get, then talk with your doctor.

Q:   I broke up with my boyfriend last november and had unprotected sex with some else twice on the 14th and the 19th of december I then had a period on the 24th of december. On the 30th me and my boyfreind got back together and had sex, now im pregnant, I need to be 100% who's baby this is.

A:   As your period was on the 24th of December, you would have become pregnant after this date.

Q:   I had a one night stand with my fellow employee. My husband returned from a business trip two weeks later. I had unprotected sex with both and I am now pregnant (10 weeks). Can I work out who the father of the baby is?

A:   If you did not get your period between the two encounters you can not be 100% positive of who the father is without paternity testing. When you have intercourse with more than one partner around the same time and a pregnancy results, it is impossible to determine who the father of the baby is based on dates.

Sperm can live inside a woman's body for 3 to 5 days. You do not know the exact date that you ovulated, so it is possible that both men's sperm were inside your body at the same time. If that were the case there is not any way to even guess which man's sperm caused the pregnancy. The only way to be certain of paternity is to have a paternity test done.

Return to Conception Calculator
The information on this page and web site is for informational purposes only,
and is not a substitute for medical diagnosis and treatment by a physician.

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