How to Calculate the Date of a Baby Creation

When calculating the date of conception of your baby, it is important to understanding that there is no way of determining the exact day on which he was conceived. The only way to have an absolute dating of the day of conception is if you've undergone in vitro fertilization, been artificially inseminated or have monitored your fertility with charting. It is also possible to conceive days after intercourse since sperm can survive in a woman's body up to five days. The first day of the most recent menstrual period is used to determine the age of the baby. For more accuracy, an ultrasound can be used in early pregnancy to confirm the age.

Instructions

Using Last Menstrual Period

• 1

  Calculate the first day of your last menstrual period. Woman with regular periods usually conceive within 11 to 21 days of that day.

• 2

  Add an additional two weeks from this date. Menstruation is the body preparing itself for pregnancy so these two weeks are considered part of the pregnancy, even though they pre-date the actual date of conception. This gives a relatively accurate estimation of the date of conception.

• 3

  Estimate the due date by adding 40 weeks from the first day of your last menstrual period. Understand that this is only a broad estimate as only about 5 percent of newborns arrive on this date.

Using an Ultrasound

• 4

  Take the date of your earliest ultrasound and the gestational age of the baby as indicated by the ultrasound. This is measured in weeks and days and is determined by measuring the size of the baby.

• 5

  Count back to week two of the pregnancy date to find the estimated conception date. For example, if the date of the ultrasound was February 28th and the age of the baby was determined to be 6 weeks, 5 days, you would subtract four weeks, five days from that date in order to arrive at the two week point. This would result in a conception date of January 26th.

• 6

  Confirm the date of your last period by comparing it with the measurement of your baby taken by ultrasound. If they do not match, it may mean the last menstrual period date is incorrect. In this case, it is necessary to determine the correct date in order to find a more accurate estimate of the date of conception.