Doctors use the first day of your last menstrual period to calculate your estimated due date, however other factors can influence the babies arrival date.
The formula to estimate the due date of a baby is calculated by adding 266 days to ovulation (Ovulation Calculator), or 280 days to the first day of your last menstrual cycle.
Human female pregnancy lasts 40 weeks on average. However do not forget that the average month is 4 weeks and several days long, not four weeks exactly. It is for this reason that doctors calculate how many weeks pregnant you are, as measuring pregnancy by weeks is a far more accurate means to determine length of pregnancy.
Read our Signs and Symptoms of Being Pregnant article.
Your babies due date can never be predicted precisely, even when the exact date of conception is known, as there are several variables that can affect the date given as your babies due date. For instance menstrual cycles can last from 22 days to as many as 44 days, so to obtain reasonably accurate results you will need to enter the average number of days in your menstrual cycle in the pregnancy calculator.
Another factor that can influence your babies birth date is the fact that you may not have conceived on the day you had intercourse! Human sperm can actually survive in a womans uterus for up to 3 days after sex. Your doctor will help you obtain the most accurate estimated date of conception or due date.
Our pregnancy calculator will provide you with a close estimate of the due date of your baby and several other interesting dates including date of conception, end of your first and second trimester, the date your child is due on, and the number of weeks you have been pregnant for. This is the way most doctors calculate a due date without an ultrasound.
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