Pregnancy Calculator

Estimates conception date, gestational age of the baby in weeks and pregnancy evolution for the current week.

The first day of your last menstrual period:
Menstrual cycle length:
  Embed  Print  Share 

Send Us Your Feedback

Steps on how to print your input & results:

1. Fill in the calculator/tool with your values and/or your answer choices and press Calculate.

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.

This pregnancy calculator uses the first day of the menstrual cycle and its average length to determine the probable ovulation date, along with the fertility window – date which offer information on the likely conception date, as well as the estimated gestational age and due date.

For the purpose of this calculator, the pregnancy definition used is the development of an embryo in a woman’s uterus started through fertilization of an egg and that culminates with birth.

In the event of fertilization occurring during ovulation or on one of the dates in the fetility window, the gestational age of the resulting pregnancy age is counted from the first day of the last menstrual cycle.

Pregnancies are divided into three trimester periods. The first trimester represents 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, which is estimated at 266 days from conception or 40 weeks from first day of the last menstrual period.

This tool also offers a detailed, week by week account of the developments in pregnancy, depending on the current week resulted in the calculation.


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

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

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

Specialty: Obstetrics Gynecology

System: Reproductive

Article By: Denise Nedea

Published On: April 13, 2020

Last Checked: April 13, 2020

Next Review: April 13, 2025