Calculating Due Dates When Pregnant

black and white Texas Instruments calculator

Although pregnancy might feel like it lasts forever, the length of a normal, full term pregnancy is 40 weeks. Despite the myth that pregnancy only last nine months, in all likelihood, a full term pregnancy will last 40 weeks.

Pregnancy Due Dates are Calculated in Two Ways

The good news about the 40-week gestational period is that the two weeks prior to conception actually count towards the 40 weeks of pregnancy. A full term pregnancy is measured from the date of the start of last menstrual period through 40 weeks.

If a due date is calculated using the date of conception, which is often known when fertility specialists are used, then the due date is 38 weeks past the date of conception.

Pregnancy Calculators are Accurate and Easy to Use

To calculate a due date, go back to the start date of the last menstrual period and count 40 weeks from that date. There are many pregnancy calculators that can be used online. A pregnancy calculator will take the guesswork out of the equation. Just type in the date of the start of the last menstrual period into a pregnancy calculator and the due date of the baby will be displayed on the screen.

Once a Period is Missed, the Pregnancy is Considered One Month Old

Since the pregnancy cycle starts at the first day of the previous menstrual cycle, by the time a period is missed the pregnancy is considered one month old. Although fertilization occurred roughly two weeks prior, the pregnancy is one month along.

Babies born after 37 weeks gestation are considered full term, although doctors prefer babies to remain in the womb as close to 40 weeks as possible. Babies born earlier than 37 weeks may need more careful observation, but in general babies born between the 36th and 37th week are fully developed and need no further follow up care.


Once a pregnancy calculator is used, a pregnancy can be followed day by day or week by week and at each stage both parents can read about how their baby is progressing through the pregnancy. Parents can view pictures of babies at every stage of development thanks to information available on many internet sites. Gender can even be established somewhere around the 20 week mark of pregnancy through ultrasound.

Sources:, *”Pregnancy Due Date”, *”Pregnancy Due Date Calculator”, *Pregnancy Due Date Calculator”