Calculator: Expected date of delivery + number of weeks of pregnancy (PW)

Using this calculator, you can quite easily determine the day the baby will be born, knowing the date of the last period. In addition to the delivery date, you will receive important information on each week of pregnancy and the trimesters. Simply enter the day of your last period and the length of your menstrual cycle and the pregnancy calendar will show you all of the important information.

Are you already pregnant? Or do you want to find out when your fertile days are?

At a Glance

  • The first day of the most recent menstruation is considered to be the start and the delivery date to be the end of the 40 weeks of pregnancy.
  • To calculate the delivery date, add 281 days to the first day of the last period.
  • Statistically speaking, only 5.54% of children come into the world on the calculated date of delivery. That means that 94.46% of children are not born on the calculated date. 90% of kids are born up to two weeks after or up to three weeks before the calculated birth date.
  • The best time to determine sex is by means of ultrasound in the 20th week of pregnancy.
  • Pregnancy tests at home using an over-the-counter test from the drug store or apothecary are reliable beginning in the 4th or 5th week of pregnancy (i.e., 1 or 2 weeks after fertilization).

Pregnancy weeks and date of delivery

Pregnancies are measured in pregnancy weeks. A normal pregnancy lasts 40 pregnancy weeks (PW for short) or 281 days. Thus, the first day of the most recent menstruation is considered to be the start and the delivery date to be the end of the 40 weeks of pregnancy.

Most women do not know the precise moment of conception; that is why, in the interest of simplicity, calculations are done from the first day of the most recent menstruation. That is, however, not quite right medically because ovulation, when an egg cell can first be fertilized, takes place only about 14 to 16 days after the start of the period.

How are weeks of pregnancy calculated?

Example: the 10th week of pregnancy means that already 9 weeks plus 1 to 7 days of pregnancy have elapsed.

9W3 = 9 completed weeks of pregnancy + 3 days =  pregnancy weeks + 3 days = 10th PW

Division of pregnancy into 3 trimesters

Besides the division into pregnancy weeks, there is yet another division: namely into the three periods known as trimesters.

Calculation of pregnancy according to Naegele’s rules

Dr. Franz Naegele discovered a method of calculating the delivery date. To use it, 281 days are added to the first day of the last period.

Calculated date of delivery

Statistically speaking, the most (5.54%) children come into the world on the calculated date of delivery. If we turn that around, it means that 94.46% of children are not born on the calculated date.

To be born up to two weeks after or up to three weeks before the calculated birth date is considered normal. This represents about 90% of all children. Children who come into the world more than three weeks before the calculated date of birth are considered to be premature (9% of all children). Children who arrive more than two weeks after the calculated date of birth are considered to be overdue (1% of all children).

90% of all children arrive in the world close to their calculated delivery date.

90% of all children arrive in the world close to their calculated delivery date.

Determining a baby’s sex

Many parents would like to know their children’s sex before birth. However, in the first few weeks of pregnancy, it is hardly possible to determine sex since all embryos look alike.

At this stage, embryos display a kind of bud, a sort of bulge (protuberance). For offspring, the female body starts to produce distinct hormones, beginning with the 8th week of pregnancy.  The bud develops into a penis or a vagina. But the formation of the sex organs is a slow process. It is only after the 12th week that it is even possible to identify the sexual organs. But predictions at this point in time are still rather uncertain. Even very experienced sonograph specialists using the best ultrasound equipment have a success rate of only about 68%. If the baby is lying incorrectly or has rolled itself up or is moving or if the sexual organ has only developed slightly, the success rate is even lower.

The best time to determine sex is by means of ultrasound in the 20th week of pregnancy. Then it is fairly simple to determine the sex since the sexual organs are clearly developed.

Determining sex is full of pitfalls. Even with modern technology and extensive experience, doctors can make mistakes.  

Determining sex is full of pitfalls. Even with modern technology and extensive experience, doctors can make mistakes.

Pregnancy: At what stage can boys and girls be distinguished?

As precise as modern ultrasound technology may be and as experienced as a doctor may be, mistakes and errors happen again and again. Thus it happens that parents report that they were mistakenly told to expect a boy because the doctor mistook the umbilical cord for a penis.

But for many parents-to-be, pregnancy is also a time of uncertainty and fear. Many parents worry about the health of the baby and naturally also about the birth itself. Against this background, getting the baby’s sex right is rather secondary in importance. It is much more important to develop a healthy positive attitude and be pleased with the prospect of having offspring.

In countries like China, India, and South Korea – but also Eastern Europe and Africa, the question of sex in these traditionally patriarchal societies has a totally different meaning. Boys are desired; girls are frowned upon. Some female fetuses are targeted for abortion (“gendercide” or “femicide”).

Pregnancy test – beginning when? Calculate the date

At the beginning of pregnancy, the body starts to produce the pregnancy hormone hCG (human chorionic gonadotropin). Six to nine days after nidation of the fertilized egg, the hormone can already be detected in the blood. The gynecologist can then carry out a blood test or by means of a special ultrasound device, detect the amniotic sac of the fetus.

Pregnancy tests are reliable after the fourth or fifth week.

Pregnancy test by means of urine – when is that possible?

Pregnancy tests at home using an over-the-counter test from the drug store or apothecary are possible, beginning in the 4th or 5th week of pregnancy (in other words, 1 or 2 weeks after fertilization). Such a test should be carried out in the morning since urine in the morning is more concentrated than it will be during the course of the day or evening. Modern pregnancy tests can detect even small amounts of the hCG hormone in the urine and are thus more than 99% accurate after the due date of the period.

How precise are early tests/pretests?

Early tests – also called Pretests – are not particularly reliable. If you want a result you can be sure about, you should wait until the fourth or fifth pregnancy week.

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