How to Calculate Pregnancy

Early pregnancy can be an exciting time with many questions, including when the baby will be born and how far along the pregnancy has progressed. There are several ways to calculate information about a pregnancy, most of which require information about the woman's last menstrual period or even the baby was conceived, if that is known. So grab your calculator, calendar and a pencil and get ready to calculate some numbers.

Things You'll Need

• Calculator
• Pencil
• Paper
• Calendar
• Computer access

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Instructions

• 1

  Look at a calendar and pinpoint the first date of the last menstrual period, if known. Count 40 weeks from that date. This is the estimated due date of the pregnancy.

• 2

  Count the weeks on the calendar from the first date of the last menstrual period to the current date. This number is the current pregnancy week. Pregnancy is divided into three trimesters, each roughly 14 weeks in length. If the date of conception is known (typically two weeks after the start of the last menstrual period), this will provide an even more accurate estimate by counting from the date of conception to the current date.

• 3

  Measure the length of the woman's belly from the breastbone to the pubic bone using a cloth measuring tape after approximately three months of pregnancy. The number of inches on the measuring tape will roughly equal the current pregnancy week.

• 4

  Ask for an ultrasound to measure the size of the fetus, as the size of the baby can be informative about the current pregnancy stage and estimated due date.

• 5

  Use online due date calculators to help you determine the estimated due date of the baby as well as the current pregnancy stage. Some websites that offer this tool include BabyCenter.com, iVillage.com and What to Expect.com (see Resources).