Pregnancy Week Calculator

Determines the pregnancy week and describes fetal development, estimates conception and due date, based on menstrual cycle data.

This pregnancy week calculator offers a series of very useful information that describes and dates a pregnancy, starting from two very simple variables:

■ First day of last menstrual period: Each period marks the start of a new cycle and this day is then taken into account for estimating ovulation, to date the pregnancy and estimate due date.

■ Menstrual cycle length – which can very between 26 and 36 days – the more regular the cycle, the more accurate the prediction.

Based on the above, the tool retrieves:

■ The probable ovulation date and the fertility window – which offer an indication of when the baby was likely conceived;

■ The estimated gestational age – this is calculated from the start of the last menstrual period;

■ The estimated due date – this is calculated as approximately 266 days from probable ovulation (based on a full-term pregnancy with delivery at 40 weeks);

■ A detailed description of the fetal changes during the current pregnancy week.

Early pregnancy signs

■ Tender, swollen breasts: similar or greater tension in the breasts, compared to pre-menstrual syndrome symptoms.

■ Nausea or vomiting: these two are some of the most common pregnancy symptoms.

■ Frequent urination: in some cases this could be early symptom but the need to urinate more definitely increases as pregnancy progresses.

■ Fatigue: the increased levels of hormones and the need for the body to sustain the physiological changes that come with pregnancy may lead to tiredness.

■ Heightened senses: a very sensible sense of smell and taste (food-cravings or food aversions).

■ Basal body temperature: those monitoring bbt in their cycles can experience a constant increased temperature for more than 14 days after ovulation.

■ Bleeding: spotting around the time when first day of period should take place, this spotting could indicate implantation bleeding but is not compulsory to occur.


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

Moore LK. (2008) Before We Are Born: Essentials of Embryology and Birth Defects. Philadelphia, PA: Saunders/Elsevier.

Hunter LA. (2009) A Simple Solution to Dating Discrepancies: The Rule of Eights. Issues in Pregnancy Dating: Revisiting the Evidence. Journal of Midwifery & Women’s Health 54 (3): 184–190.


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