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How to Calculate When You Conceived

Often, when women find out they are expecting they want to know when they conceived. Women want to know their conception date for many reasons, one of which is to determine their due date. It is impossible to determine an exact conception date, but you can determine a narrow window.

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  1. Look at your calendar to figure out the first day of your last period. Pregnancy is around 40 weeks in duration beginning the first day of your last period. Knowing the date of your last period will help you determine your conception date and due date.

  2. Calculate conception by determining when ovulation takes place for you. If you have a normal 28 day menstrual cycle, conception occurs about two weeks after the first day of your last period. According to the American Pregnancy Association, on average, a woman with a 28 day cycle ovulates anywhere between 11 and 21 days from the last menstrual period or from 12 to 16 days from when next menstrual period is expected to start. Women with irregular cycles may need to rely on other methods to calculate ovulation including the use of an ovulation kit, evaluating cervical mucus or calculating basal body temperature.

  3. Consider when you had intercourse. Having intercourse around the time you ovulated can result in conception. Remember sperm can live three to five days, so your conception date may be an estimate.

  4. Count 266 days from the date of conception to get a more exact due date, according to

  5. Tip

    Using an ovulation kit can help you better predict when you ovulate.


    Conception dates are only estimates.

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Things You'll Need

  • Calendar

About the Author

Hillary Marshall has been writing professionally since 2006. Before writing instructional articles online, she worked as a copywriter and has been published in "Ideal Living" "Sass" "Science Edge" and "Shopping Cents" magazines along with countless websites including Gadling a blog by the Huffington post. Marshall studied early childhood education at the Stratford Career Institute.

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