Pregnancy Week Calculator: Calculating the week of pregnancy with a descriptive calendar

Updated on by Stefan Banse

Calculate your current week of pregnancy. You will receive important information about how many weeks and days you have already completed and how many weeks of gestation you are in.

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Sample calculation and topic overview of the Pregnancy Week Calculator

Calculator  ↑ Content  ↑Help tips of the Pregnancy Week Calculator

A pregnancy calendar with numerous important dates starting with the fertilization date, dates for preventive medical check-ups, key stages of the baby's development up to the calculated date of birth round-off of the Pregnancy Week Calculator in terms of content. The Pregnancy Week Calculator requires the following entries to calculate the current week of pregnancy:

The first day of the last period

The weeks of pregnancy are counted from this point on. This is because the duration of pregnancy in medicine is measured from the first day of the last menstruation, although the actual pregnancy (depending on the duration of the cycle only occurs about 2 weeks later with fertilization following the ovulation. From fertilization, a pregnancy lasts an average of 38 weeks. Together with the 14 days that usually elapse between the first day of the period and fertilization, the average pregnancy lasts for 40 weeks.

Additional entry: average duration of the cycle

This information can be used to calculate the expected date of birth in addition to the current week of pregnancy, which you will find in the result under “Important Dates”. This is a 28 day cycle of 40 weeks or 280 days after the first day of the last period and shifts forward or backward by the corresponding days in the case of a deviating cycle.

Calculator  ↑ Content  ↑Examples showing the calculation of the week of pregnancy with the Pregnancy Week Calculator

Mrs Klein’s wish to have a child finally comes true; Her Pregnancy test is positive. Today on November 3, 2021, she wants to calculate in which week is her pregnancy. She would like to know the expected date of birth and important information about the development of her child and the dates of the check-ups.

  • Mrs Klein's first day of her last period was on September 20, 2021.
  • Mrs Klein's cycle length is regularly 28 days.

Calculator  ↑ Content  ↑Calculation of the week of pregnancy

Mrs Klein's first day of her last period was 44 days ago.

As described above, the duration of a pregnancy is already determined from the first day of the last menstruation. This reference date forms week 0 with day 0, hence this marks the beginning of the first week of her pregnancy.

For Mrs Klein, 6 weeks and 2 days are already complete. Therefore, she is 7 weeks pregnant.

Note: Since Week 6 of her pregnancy has been completed, she is currently in her 7th week. Therefore, Mrs Klein is in the 7th week of pregnancy. Sometimes, this confusing fact should be taken into account in practice. There are two common variants for naming the week of pregnancy. One is by completed weeks and the other is by unfinished weeks. In this example, Mrs Klein is 6 weeks and a few days pregnant. Therefore, she has already completed Pregnancy Week 6. This is referred to as an unfinished week (Week 7), which is the week she is currently in. All of these are always broken down individually as the concrete case in the result of the Pregnancy Week Calculator in the info text for the pregnancy week.

Calculator  ↑ Content  ↑Calculation of the pregnancy calendar - fertilization

In addition to calculating the week of pregnancy, the Pregnancy Week Calculator also provides a pregnancy calendar on the following important dates of pregnancy.

Calculating the date of fertilization

Fertilization or conception (i.e., the time when the sperm and egg fuse) takes place around 14 days before the next menstrual period begins.

Therefore, based on Mrs Klein's 28-day cycle, fertilization has occurred 14 days after the start of the last period (i.e., on October 4, 2021).

Calculator  ↑ Content  ↑Calculating the earliest date for a pregnancy test

With modern tests today, pregnancy can be detected before the possible next menstrual period.

As early as 13 days after fertilization (i.e., from October 17, 2021), Mrs Klein can perform a reliable pregnancy test.

Calculation of the date of the initial examination

If the pregnancy test is positive or if the menstrual period does not occur within that month, Mrs Klein needs to go for her first preventive medical check-up as soon as possible. Here, the pregnancy is determined and a comprehensive examination of the expectant mother is carried out.

Mrs Klein should have her first preventive medical check-up immediately.

Calculation of the date of the child’s heartbeat

Starting from the 5th week of pregnancy, the baby's heart already begins to beat.

Mrs Klein's baby's heart could have been beating since October 19, 2021.

Calculation of date of organ plant

From the 8th week of pregnancy, all the child's internal organs are already laid out.

Mrs Klein's child's internal organs are fully laid out from November 9, 2021.

Calculator  ↑ Content  ↑Date calculation of sex determination

From the 16th week of pregnancy, the sex of the child can be determined by ultrasound.

Mrs Klein will be able to find out whether it is a boy or a girl from January 4, 2022.

Calculator  ↑ Content  ↑Date calculation of noticeable movements

Between the 18th week of pregnancy and the 20th week of pregnancy, the time begins when Mrs Klein may already be able to feel the first movements of her child in her belly.

Mrs Klein will probably be able to feel the first movements of her child from January 18, 2022.

Date Calculation of Development Hearing

Between the 23rd and 25th week of pregnancy, the inner ear is fully formed or developed. Your child can now hear you and sometimes reacts to sounds from outside.

From February 22, 2022, Mrs Klein's baby can start hearing.

Calculation of deadline for finished development

Between the 30th and 34th week of pregnancy, the child is fully developed. It continues to grow and gain weight until birth.

As of April 11, 2022, Mrs Klein's pregnancy has progressed to the point where her baby-to-be is fully developed.

Calculator  ↑ Content  ↑Calculation of the date of birth

The expected date of birth is exactly 40 weeks after the first day of the last period in a 28-day cycle. As the individual time periods slightly vary from woman to woman, the gynaecologist may still correct the expected date of birth in the course of the pregnancy. If you have any question or doubts, please contact your gynaecologist. In advance, you are welcome to use our Birth Date Calculator.

Mrs Klein's calculated due date is June 26, 2022.

Calculator  ↑ Content  ↑How is the child developing during the respective weeks of pregnancy?

Pregnancy is one of the most beautiful experiences in a woman's life. One's own body changes and offers the growing baby a sense of security and protection until it is born. For us humans, it takes 40 weeks until birth. During this time, the foetus registers all the movements of the mother, feels moods and stress and perceives sounds. Every single day in the womb is important for the development of the unborn child's organs.

What happens in the first 3 weeks of pregnancy?

Pregnancy begins at the time of conception; this often cannot be determined exactly. Therefore, the calculation of the weeks of pregnancy usually starts on the day of the last female cycle (i.e., the beginning of the last menstrual period). In the second or third week of the cycle, ovulation takes place (now the woman is ready to conceive). The egg remains capable of fertilization for 24 hours, male sperm have a life span of 72 hours. If a sperm reaches an egg and penetrates its membrane, fertilization is successful. The egg then travels through the fallopian tube into the uterus.

What happens in the 4th week of pregnancy?

At the beginning of the fourth week of pregnancy, the embryo is just one millimetre in size. The pregnant mother now secretes more of the hormone progesterone, and the first symptoms may occur. A pregnancy test at this time provides a reliable result.

What changes in the 5th week of pregnancy?

The embryo is now in the third week of life when the heart begins to beat, and is about the size of a seed. From this moment on, it transfer blood and thus oxygen and nutrients from the mother into its own body. Then the foetus also reacts sensitively to external influences (e.g., the consumption of alcohol or nicotine). The first organs are now also laid out. The so-called neural tube, which later forms the spinal column, head and spinal cord, is closed.

What changes take place in the 6th and 7th week of pregnancy?

Now the embryo is growing rapidly by about a millimetre a day. The shape of the head and upper body is forming, the brain is developing, and the digestive tract is emerging. By the end of the seventh week, the lungs, liver, kidney and internal sex organs are formed. Legs, arms and almost paddle-like hands can already be seen in the ultrasound. The face with nose and eye sockets is also formed. The first muscle strands develop and the embryo begins to move.

How is the child developing in the 8th week of pregnancy?

The mother's pregnancy now becomes visible towards the end of the second month, mainly through changes in the breast. The embryo is now about two centimetres in size. In its body, the individual organs have found their place, and the brain has formed different parts. The heart now has all four ventricles and performs about 160 beats per minute.

How does the embryo change in the 9th week of pregnancy?

All the internal organs have now been formed and are starting to work. The first nerve cells are also already functioning. In the foetus (also known as the embryo), the fingers, toes, ears and eyelids have been laid out as well as arms and legs. The brain is protected by solid skull bones, but they are still only loosely joined together by fontanelles.

What developments take place in the 10th and 11th week of pregnancy?

The unborn baby now weighs about 4 grams and is the size of a plum. The eyes have been laid out. The embryo can also bend its arms and legs and clench its fists. There are webbed toes and fingers, but these will disappear. Finger, toenails and tooth buds are formed. The thorax closes, new layers of skin cover the tiny body, and the lanugo hair is also formed. It warms the embryo and protects it in the amniotic fluid.

What happens in the 12th week of pregnancy?

The development of the mother's placenta is now complete and the embryo is completely supplied by it. In the following period, the foetus continues to grow and move more often. Afterward, its reflexes develop. It can swallow amniotic fluid and already suck its thumb. In addition, he is already passing urine, so the mother has to change the amniotic fluid frequently.

What changes take place in the 13th and 14th week of pregnancy?

The unborn baby now weighs about 20 grams and is about 7 centimetres tall. Its organs continue to mature and the intestines are fully formed. The embryo has its first bowel movement. The skeletal cartilage changes into bones, and now it also receives sounds in the womb. The unborn baby even reacts to touches on the abdomen and turns its head in the corresponding direction. Its metabolism is now becoming more and more active. The embryo perceives very bright light as red in the mother's womb. In an ultrasound examination, the sex of the child can now also be determined.

What happens in Week 15 and 16 of pregnancy?

The weight of the embryo has now increased to up to 60 grams, and now measures a good 10 centimetres from head to rump. At this stage, the embryo is moving very actively, raising its head, turning it and even nodding. By the end of the fourth month of pregnancy, the grasping reflexes are pronounced, and some babies hold the umbilical cord in their hands. It exercises its lungs and breathing by breathing in and releasing amniotic fluids.

What happens in the 5th month?

The child continues to grow in the womb and its organs mature. With active movements, the embryo trains its muscles. Its sebaceous glands release the so-called cheese gunk, which protects the skin from softening. In addition, the subcutaneous tissue is now building up.

What changes in the child take place in week 22 to 24 of pregnancy?

From this second point onwards, the growth in length decreases and the baby gains more weight. Its weight has now increased to about 450 grams, and the unborn baby is about 20 centimetres tall. The fetal hearing has improved so much that he can distinguish the voices around him. In the 24th week, the windpipe forms, and the alveoli and blood vessels also develop.

What happens in the 25th week of pregnancy?

From this point onward, newborns today have a chance of surviving, even if the lungs have not yet matured. The foetus now weighs about 800 grams and measures 30 centimetres from head to toes. In the coming week, the child opens its eyes for the first time. In addition, his brain continues to structure itself. It reacts to loud voices and to stroking of the belly. In this way, the bond between mother and child is already strengthened in the womb. Towards the end of the sixth month, the baby perceives the differences between light and dark and begins to dream.

How does the embryo develop during Pregnancy Week 29 to 33?

The baby is moving vigorously, and bumps on the womb show the position of the arms, legs or bottom. At this stage, some babies are already starting to turn. With the head down, they take the birth position. At 40 centimetres tall and weighing around 1,400 grams, the unborn baby fills the womb well. Therefore, it assumes the typical curved foetal position. In addition, it now takes control of its own body temperature. The sensation of pain also develops. The unborn baby now orients its waking phases to the mother's day and night rhythm.

From the 38th week the waiting for the birth begins

At this week, the child is now fully developed. With the rupture of the membranes, birth is initiated. In the 40th week of pregnancy, the baby weighs about 3,500 grams and is 50 centimetres tall. Some are in a hurry and come as early as the 39th week, while others take their time. However, only when the calculated date of birth is more than 10 days is there a cause for concern.

Support during pregnancy

The optimal development of the child and the health of the mother is monitored by various medical examinations during pregnancy. Not only ultrasound plays a role, but it also performs special checks such as a nuchal fold­­measurement or amniotic fluid­examination. A trusting relationship between the pregnant woman and her chosen gynaecologist is particularly important at this time. Birth­preparation courses and timely contact with a midwife are also on the programme of expectant parents.

Source information

As source for the information in the "Week of pregnancy" category, we have used in particular:

Last update on November 4, 2021

The last changes in the "Week of pregnancy" category were implemented by Stefan Banse on November 4, 2021. The main changes were: