Conception date calculator - calculate date/day of conception Calculate probable period of conception
Please enter the child's birthday:
By using your child's birthday we will calculate the conception date. The day of conception will be calculated based on the duration of an average full term (267 days). Calculating the date of conception this way is more accurate than recursively applying Naegele's rule. After calculating the conception date, you will get, alongside your result, more detailed information about it and how to interpret it. In case you have access to information about the course of the pregnancy, you may enter it subsequently to readjust the calculation for accuracy.
Calculation based on this birthday:
The conception of this child was around . The date is calculated based on the duration of an average full term (267 days). This is correct for about 10% of all babies. [, , ]
With a very high probability the conception took place between and . This is the time span for full-term babies. For about 90% of all newborns the delivery is at term. [, ]
If the birth of this child has been a preterm delivery, conception was after . A preterm or premature delivery is when the baby is born before the 37th week of pregnancy. For about 6% to 9% of all newborns the delivery is preterm. [, ]
If the childbirth was postterm, conception was before . Any pregnancy called overdue or postterm/post-date means that the baby is born after the 42nd week of pregnancy. For about 1% to 3% of all newborns the delivery is postterm. [, ]
Why would one require the conception date today, when DNA tests are available showing the statistical probability of the child's patronage? If you are the mother: If there is any necessity for paternity establishment, there are reasons to define the probable period of conception. Your testimony regarding your sexual activity with the alleged father must be given some biological relevance to the birth of the child and a period of time must be established to limit the alleged father's evidence regarding your potential sexual activity with other men. Testimony of sexual intercourse between you and the alleged father during the probable period of conception is crucial to the case. If you are the alleged father: Even if a blood or a genetic test shows a probability of 99% or higher it doesn’t mean that you are the biological father without any doubt. If you (the putative father) for example can show you had no access to the child’s mother or were sterile during the probable period of conception, you may still attempt to rebut your paternity.
The calculated dates and time spans above are based on biological facts. To inform yourself of the legal probable period of conception defined by your jurisdiction, please contact a lawyer. The following is an example based on the jurisdiction of Wisconsin, U.S.A. (probable period of conception defined from 240 to 300 days before delivery) . Under these circumstances the probable period of conception is between and . 
The period of conception may be narrowed down by taking the given gestation week at birth into consideration. You may find this information on the child's maternity card.
The figure denoting the gestation week will be broken up into two parts. The left part represents the week and the right part the day of this week.
Commonly the gestation age counts the days of pregnancy after a woman's last normal menstrual period and, in this case, is called the gestational week. It is less common that these digits represent embryonic or foetal-age. This is more precise but not commonly used in obstetrics.
If gestational or embryonic age is not indicated or specified, then the gestation week represents gestational age.
Gestation week on delivery:
Calculation based on the birthday:
and delivery at gestation week ()
Conception took place around .
Here, gestation week at delivery is expressed as gestational age. So, the days from the first day of pregnancy until delivery were counted beginning at the first day of the woman's last normal menstrual period prior to pregnancy. This means conception could have taken place between 1 week before and 1 week after the conception date stated above.
If this pregnancy was closely followed by doctors, regular check-ups and ultrasound examinations of the unborn baby, then the date above is precise. The ultrasound examinations during pregnancy in particular are used to adjust the gestation week based on average data of foetal intrauterine development. If there were no ultrasound examinations on a regular basis, one must widen the probable period of conception to +/- one week to the date above. But even with regular ultrasound examinations there still exists a probability of inaccuracy. Not every baby develops in the exact same way. To get more details on this probability please contact the doctor who resided over this pregnancy.Usually, if gestation week on delivery is expressed as foetal age, the day of conception is well known, therefore there is little to none uncertainty about the conception date.
Should you be surprised to find that the day of conception is 2 weeks ahead of your speculations, please keep in mind that the so-called normal duration of a pregnancy, 40.1 gestation weeks, is expressed in gestational age. The day of conception in any pregnancy expressed in gestational age, is at week two. Therefore the so-called normal duration of any pregnancy expressed in foetal age is 38.1.