This pregnancy calculator estimates the date of conception, the gestational age of the baby and the changes during the current week. Discover below the form the transformations that happen during the three semesters of pregnancy.

The first day of your last menstrual period: *
Menstrual cycle length: *

How does this pregnancy calculator work?

This health tool uses the length of the menstrual cycle and the start of the latest period to determine essential data of the cycle and also of the existent pregnancy.

The result comprises of the ovulation date and the fertility window which could be considered as one of the days in which the conception took place, an estimated gestational age of the pregnancy as well as the estimated due date for a term pregnancy. The gestational age will then be used to reveal the week of pregnancy and the changes that are happening within that period.

Example pregnancy calculation:

For instance, in a pregnancy within a cycle of 28 days with the last period starting on September 7th 2014 and the current date being November 27th 2014 the result is:

■ The probable ovulation date is September 22nd, 2014;

■ The fertility window is between September 18th and September 26th, 2014;

■ The estimated gestational age 11 weeks and 3 days;

■ The estimated due date is June 14th, 2015.

Week 12: During this week your baby's brain continues to develop. Vocal cords are formed and fingernails and toenails start to form. Intestines make their way into the abdomen to their final place and kidneys start to function using the amniotic fluid the baby swallows. This week is the last of the first trimester; you will be in a few days entering the second trimester.


This period represents the development of an embryo in a women's uterus, process that ends with the birth of one or more offspring. This process begins with the fertilization, the moment of fusion between the male sperm and the female egg.

The date of conception depends on the female body menstrual cycle as the fusion can only take place when one egg is matured and released from the ovary and this only happens half way through the menstrual cycle at a date called ovulation date.

A successful conception can only take place at a range of a few days before and after ovulation. This explains why the pregnancy calculator asks you to enter your last menstrual period and the length of your menstrual cycle. This data is necessary to determine a probable ovulation date and some possible conception dates.

In the event of a fertilization the resulting pregnancy age is counted from the first day of the last menstrual cycle. In the next lines we'll discuss how a pregnancy period is divided and the development of the future baby in each of these periods of time.

The developing offspring is called embryo for the first 8 weeks following conception and then called fetus for the time remaining till birth. In many medical societies human pregnancy is divided into three trimester periods but can also be analyzed through each week's developments.

The pregnancy trimesters

The first trimester represent the period between the first and fourteenth week and follows the development of the embryo into a fetus.

The second trimester represents the period between the fourteenth week and the twenty-seventh week, continues the development of the fetus

The third trimester represents the period between the twenty-seventh week and the birth date. In this time the baby grows the most in weight and height and all bodily functions are ready to work independently of the mother in case of birth.

The estimated due date is the date in which the birth will take place in the event of a normal pregnancy that began in one of the conception dates. This due date is an estimate of approximately 266 days from the conception.

Should also be taken in consideration that not all pregnancies are terminated with birth at exactly 40 weeks. Statistics say that 20% of women give birth in week 38, 20% in week 39, 30% give birth in week 40 and 20% in week 41.


1) Sadler TW, Langman J. (2012) Medical embryology. 12th ed. Philadelphia : Wolters Kluwer Health/Lippincott Williams & Wilkins

2) Wylie L. (2005) Essential anatomy and physiology in maternity care 2nd ed. Edinburgh: Churchill Livingstone.

3) The Johns Hopkins University School of Medicine Department of Gynecology and Obstetrics. (2012) The Johns Hopkins Manual of Gynecology and Obstetrics 4th ed. Lippincott Williams & Wilkins

05 Dec, 2014